SAN FRANCISCO (AP) — A law enforcement official says the weapon used in the shooting death of a woman on a San Francisco pier belonged to a federal agent — the latest twist in a case that has become a flashpoint in the country's debate over immigration. 
 
 San Francisco Public Defender Jeff Adachi, left, talks to members of the media after Francisco Sanchez' arraignment Tuesday, July 7, 2015, in San Francisco. Prosecutors have charged Sanchez, a Mexican... (Associated Press) 
 
 Assistant Director of Field Operations, Enforcement and Removal Operations at the?U.S. Immigration and Customs Enforcement at the Department of Homeland Security Philip T. Miller testifies before the... (Associated Press) 
 
 San Francisco Sheriff Ross Mirkarimi gestures during an interview Monday, July 6, 2015, in San Francisco. Mirkarimi has defended the release of Francisco Sanchez from jail on April 15, who is now accused... (Associated Press) 
 
 Senate Homeland Security and Governmental Affairs Committee Chairman, Sen. Ron Johnson, R-Wis., left, shakes hands with Associate Director of Refuee, Asylum, and International Operations at U.S. Citizenship... (Associated Press) 
 
 Francisco Sanchez, center, is lead out of the courtroom by San Francisco Public Defender Jeff Adachi, right, and Assistant District Attorney Diana Garciaor, left, after his arraignment at the Hall of... (Associated Press) 
 
 Francisco Sanchez walks into the court for his arraignment at the Hall of Justice on Tuesday, July 7, 2015, in San Francisco. Prosecutors have charged the Mexican immigrant with murder in the waterfront... (Associated Press) 
 
 San Francisco Public Defenders Jeff Adachi, left, and Matt Gonzalez, right, talks to members of the media after Francisco Sanchez' arraignment Tuesday, July 7, 2015, in San Francisco. Prosecutors have... (Associated Press) 
 
 FILE - This undated photo provided by the San Francisco Police Department shows Francisco Sanchez. The fatal shooting of a woman at a sightseeing pier has put San Francisco under an uncomforable and nasty... (Associated Press) 
 
 The official, who had been briefed on the matter, said Tuesday that a check of the gun's serial number shows it belonged to a federal agent. 
 
 The official — who was not authorized to speak publicly about the case and spoke on condition of anonymity — declined to elaborate. 
 
 The San Francisco Police Department, which is investigating the case, refused to comment on the disclosure. 
 
 The suspected gunman, Juan Francisco Lopez Sanchez, has been deported to his native Mexico five times and is suspected of living in the United States illegally when Kathryn Steinle, 32, was gunned down last week while on an evening stroll with her father along San Francisco's popular waterfront area. 
 
 Federal officials transferred Sanchez to San Francisco's jail in March to face a 20-year-old marijuana charge after Sanchez completed his latest prison term for illegally entering the country. 
 
 The San Francisco sheriff, citing the city's "sanctuary city" policy, released Sanchez in April after prosecutors dropped the drug charge, despite an Immigration and Customs Enforcement request to hold him for federal authorities so deportation proceedings could begin. 
 
 Sanchez pleaded not guilty Tuesday to first-degree murder. 
 
 He told two television stations who interviewed him in jail that he found the gun used in Steinle's killing wrapped in a shirt on the pedestrian pier she was walking on. Sanchez said the gun went off in his hands, and his public defender, Matt Gonzalez, said Tuesday that the San Francisco woman's death appeared accidental. 
 
 Regardless of the reason behind Steinle's death, the shooting has touched off criticism from leading Republican lawmakers — and from top Democrats, including both of California's U.S. senators. 
 
 Democratic presidential candidate Hillary Clinton told CNN that San Francisco was wrong to ignore the ICE detainer request and release Sanchez from custody. 
 
 "The city made a mistake, not to deport someone that the federal government strongly felt should be deported," Clinton said. 
 
 Sen. Dianne Feinstein called on San Francisco Mayor Ed Lee to start cooperating with federal immigration officials who want to deport felons such as Sanchez. 
 
 "I strongly believe that an undocumented individual, convicted of multiple felonies and with a detainer request from ICE, should not have been released," Feinstein said. 
 
 The mayor's office said it has reached out to Homeland Security officials to determine if there's a way to cooperate while still upholding the city's sanctuary policy. 
 
 "Mayor Lee shares the senator's concerns surrounding the nature of Mr. Sanchez's transfer to San Francisco and release," said Christine Falvey, a spokeswoman for the mayor. 
 
 Democratic Sen. Barbara Boxer, also from Northern California, said she asked Gov. Jerry Brown if state law was followed in Sanchez's release. 
 
 "For decades, I have supported deporting violent criminals, and I have always believed that sanctuary should not be given to felons," Boxer said. 
 
 San Francisco Sheriff Ross Mirkarimi has defended Sanchez's release and the city law requiring it to ignore ICE detainer requests. The sheriff said ICE could have obtained a warrant or court order to keep Sanchez in custody. 
 
 "ICE knew where he was," Mirkarimi said Monday. 
 
 State and federal Republicans, meanwhile, said they would look into the matter. 
 
 Wisconsin Sen. Ron Johnson, who chairs the Senate's homeland security committee, criticized federal officials and demanded to know why Sanchez was not deported. 
 
 "Does that make any sense to you?" Johnson demanded to know at a hearing Tuesday. "Because I'll tell you it doesn't make any sense to the American public." 
 
 Republican state Sen. Jeff Stone said he would introduce legislation in Sacramento to require cities to comply with ICE detainer requests. 
 
 At Sanchez's arraignment Tuesday, prosecutor Dianna Garcia argued against releasing Sanchez on bail, saying, "This was an act of random violence, shooting an innocent victim in the back." 
 
 The judge set bail at $5 million, which Gonzalez said will keep Sanchez jailed pending trial. 
 
 ___ 
 
 Associated Press writers Amy Taxin in Los Angeles, Janie Har in San Francisco and Erica Werner in Washington contributed to this report. ||||| Defendant pleads not guilty in Pier 14 killing 
 
 San Francisco Public Defender Jeff Adachi, (left) leads Juan Francisco Lopez-Sanchez, into the Hall of Justice in San Francisco, Calif. on Tues. July 7, 2015, for his arraignment on suspicion of murder in the shooting death of Kate Steinle on San Francisco’s Pier 14 last Wednesday. less San Francisco Public Defender Jeff Adachi, (left) leads Juan Francisco Lopez-Sanchez, into the Hall of Justice in San Francisco, Calif. on Tues. July 7, 2015, for his arraignment on suspicion of murder in the ... more Photo: Michael Macor / The Chronicle Buy photo Photo: Michael Macor / The Chronicle Image 1 of / 12 Caption Close Defendant pleads not guilty in Pier 14 killing 1 / 12 Back to Gallery 
 
 The man accused of fatally shooting a stranger who was walking with her father on San Francisco’s Pier 14 pleaded not guilty to murder Tuesday, as his attorney argued that the evidence points to a tragic accident. 
 
 Juan Francisco Lopez-Sanchez, whose age is listed as 45 by police and 52 in jail records, made his first appearance in court, listening intently as Judge Daniel Flores read the charges against him in connection with the shocking death of 32-year-old Kathryn Steinle. 
 
 The circumstances of Steinle’s killing remained unclear Tuesday, but police have learned that the gun had been stolen just days earlier from a federal agent, according to sources close to the investigation. 
 
 Lopez-Sanchez, asked for his plea through a Spanish interpreter, answered “no culpable” and repeated the statement throughout the short hearing, even when he was not asked. He didn’t appear to understand what was happening, saying again that he was not guilty in Spanish in response to a question by the judge regarding his next court appearance. 
 
 Steinle had been walking along Pier 14 on the busy Embarcadero with her father when she was shot through the heart at about 6:30 p.m. on July 1. 
 
 Interview in English 
 
 In a jailhouse interview with KGO, Lopez-Sanchez appeared to admit to firing the shot, saying the gun went off after he found it wrapped in a T-shirt under a bench — and after he took sleeping pills he found in a trash can. 
 
 But outside court, Public Defender Jeff Adachi, whose office is representing Lopez-Sanchez, suggested that the defendant did not understand what he was being asked during the television interview. 
 
 “That interview was done primarily in English by a reporter,” he said. “I think certainly, that interview raised a lot of questions about whether Mr. Sanchez understood what was being asked.” 
 
 Lopez-Sanchez’s lawyer, Matt Gonzalez, the chief attorney in the public defender’s office, said his client has a second-grade education. 
 
 “This very well could be a completely accidental discharge of a firearm,” he said. “You’ve got an individual who does not know the victim in the case, has no interest or desire in injuring her in any way, and no witness or anybody to allege that there was any crime going on at the time the shooting occurred.” 
 
 Lopez-Sanchez was also charged with using a gun, which could add up to 10 years to his sentence if he is convicted of murder. 
 
 The .40-caliber pistol that investigators believe Lopez-Sanchez fired had been stolen from a federal agent in a car burglary in San Francisco in late June, said one source, speaking on condition of anonymity because he was not authorized to talk about the case publicly. 
 
 Other sources said the weapon — which Lopez-Sanchez allegedly dumped in the bay before it was recovered — was apparently not the agent’s official gun. 
 
 Steinle’s death sparked outrage after it was revealed that Lopez-Sanchez had a long history of drug crimes and had been deported five times to Mexico, but was recently released from San Francisco County Jail rather than being turned over to federal immigration agents for a potential sixth deportation. 
 
 He was brought to San Francisco in March after serving 46 months at a federal prison in Victorville (San Bernardino County) for felony re-entry into the country. He had an old, outstanding warrant in the city, alleging that he fled marijuana charges in 1995. 
 
 According to court records, the case was old enough that the evidence had been purged by the time Lopez-Sanchez appeared in court on March 27. Prosecutors discharged the case, and Lopez-Sanchez remained in County Jail until April 15, when the Sheriff’s Department released him without alerting immigration. 
 
 U.S. Immigration and Customs Enforcement officials said they had asked to be notified before Lopez-Sanchez’s release, so they could seek to deport him again. 
 
 S.F., state policy 
 
 The Sheriff’s Department said it had followed its own policy in not holding Lopez-Sanchez for immigration agents, as well as a 2013 city ordinance and a state law signed the same year by Gov. Jerry Brown. 
 
 Steinle’s parents did not attend Tuesday’s arraignment, but an uncle who was present shook and rocked during the proceedings and scoffed as Lopez-Sanchez declared he was not guilty. The uncle declined to comment outside court. 
 
 Gonzalez implored the media to look past the immigration debate raised by the case at the “ubiquitous nature of guns in our society.” 
 
 “Every day in the United States, innocent people die from gun accidents,” he said. “In contrast to that, I can say there are numerous studies that immigrants are far less likely to commit acts of violence than native-born persons.” 
 
 When asked about the immigration issue, Alex Bastian, a spokesman for the district attorney’s office, demurred and said, “Today’s about Kate.” 
 
 “It’s about this incredible family that has shown such strength during this incredibly difficult time,” he said. “It’s about bringing justice to that family and it’s about doing everything we ethically can to prosecute this case and bring the justice this family rightfully deserves.” 
 
 Assistant District Attorney Diana Garcia asked that Lopez-Sanchez be held without bail, while Gonzalez argued that he had the right to bail, even if he would not be able to afford it. 
 
 Judge Flores then set bail at $5 million after the prosecutor requested $10 million. Lopez-Sanchez is scheduled to return to court July 27. 
 
 Chronicle Staff Writer Jaxon Van Derbeken contributed to this story. 
 
 Vivian Ho is a San Francisco Chronicle staff writer. E-mail: vho@sfchronicle.com Twitter: @VivianHo ||||| Authorities are investigating whether a gun associated with a Bureau of Land Management employee was used in the fatal shooting of a young woman on a tourist-heavy San Francisco pier, an agency spokesperson said. 
 
 "The matter is under investigation, and law enforcement is working to confirm the origin of the weapon," the spokesperson said in a statement. 
 
 Sources familiar with the investigation say the gun belonged to a federal agent and may have been stolen recently. It is unclear whether the firearm was a government-issued service weapon or a personally owned gun. 
 
 A lawyer for suspect Francisco Sanchez said at a Tuesday arraignment hearing that Sanchez meant the victim, Kate Steinle, 32, no harm. 
 
 "There is no motive whatsoever for this defendant to have caused any harm to the deceased," public defender Matt Gonzalez said in court. "He did not know her." 
 
 Gonzalez said it is "very likely that this was an accidental shooting." 
 
 Sanchez, 45, pleaded not guilty to murder and was held on $5 million bail, according to court records. He has been charged with one count of murder with enhancements for the use of a firearm, according to court records. 
 
 Sanchez will be back in court July 27, according to court records. 
 
 Earlier this week, Sanchez told ABC station KGO-TV in a jailhouse interview that he started wandering on Pier 14 Wednesday, July 1 after taking sleeping pills he found in a dumpster. He said he then picked up a gun that he found and it went off. 
 
 Courtesy of Steinle family 
 
 The case has sparked a debate about illegal immigration because Sanchez, an undocumented immigrant, has been deported several times to his native Mexico and Immigration and Customs Enforcement blamed the San Francisco police for not honoring an immigration detainer earlier in the year. 
 
 Sanchez has five previous convictions for re-entry after deportation, according to court records. He was on probation in Texas at the time of the shooting and served federal time for sneaking back into the country. 
 
 In an exclusive jailhouse interview, a KGO-TV reporter asked the alleged gunman, "Did you keep coming back to San Francisco because you knew that they wouldn't actively look for you to deport you?" 
 
 Sanchez responded, "Yes." 
 
 U.S. Immigration and Customs Enforcement had said in a statement that Sanchez was turned over to the San Francisco Police Department this past March on an outstanding drug warrant, and that the department requested that police notify Immigration and Customs Enforcement prior to his release so ICE officers could make arrangements to take custody. 
 
 However, the San Francisco Sheriff's Department said that it had no "legal basis" to hold Sanchez based on a federal immigration detainer, according to the Associated Press. A lawyer for the sheriff's department told the AP the city only turns over illegal immigrants if there's an active warrant for their arrest, so on April 15, after the local drug case closed, Sanchez was released. 
 
 In a statement Monday, San Francisco Mayor Edwin Lee said the city's sanctuary policy "should not create a safe harbor for convicted, violent felons." 
 
 "I am concerned about the circumstances that led to the release of Mr. Sanchez," Lee's statement added. "All agencies involved, federal and local, need to conduct quick, thorough and objective reviews of their own departmental policies and the decisions they made in this case." 
 
 The San Francisco police union spoke out against the sanctuary policy, writing on its Facebook page Monday. 
 
 "A young innocent woman has been murdered in cold blood," the statement said. "He is an illegal alien not an undocumented immigrant and if he was where he belonged (Mexico) this innocent victim would still be alive."
– Another twist in the Francisco Sanchez case: The gun that the murder suspect claims he found wrapped in a T-shirt on a bench belonged to a federal agent and was stolen in a recent car break-in, sources tell the San Francisco Chronicle. The sources say the firearm wasn't the agent's official gun, and ABC News reports that the Bureau of Land Management is investigating whether the gun belonged to one of its employees. Sanchez, who claims the gun went off accidentally when he picked it up, killing 32-year-old Kathryn Steinle, pleaded not guilty to first-degree murder yesterday, the AP reports. Sanchez has been deported from the US five times, and San Francisco's decision not to turn him over to federal authorities for deportation when a drug charge was dropped in April has been strongly criticized by lawmakers and presidential candidates, including Hillary Clinton, who told CNN yesterday that the "city made a mistake, not to deport someone that the federal government strongly felt should be deported." At yesterday's hearing, Sanchez's public defender said the shooting appeared accidental and argued that the media should look at the "ubiquitous nature of guns in our society" instead of the immigration issue, the Chronicle reports.