BOSTON—Lawyers for James "Whitey" Bulger used an admitted corrupt FBI agent Friday to suggest to the jury at Bulger's racketeering trial that he was not an FBI informant, a key contention of prosecutors.

John Morris, an ex-agent who admitted taking $7,000 in cash and two cases of wine from Bulger, was grilled by Bulger's lawyer about a 700-page file the FBI filled with information Bulger allegedly gave them while an informant in the 1970s and '80s.

Morris, who received immunity from prosecution, said he accepted gifts from Bulger while former agent John Connolly—who Morris supervised—was Bulger's FBI handler.

He acknowledged that he panicked when Bulger and his partner, Stephen "The Rifleman" Flemmi, were indicted in 1995 because he knew his acceptance of bribes from Bulger could be exposed.

"I was worried about whether I could be prosecuted," Morris said. "I certainly did not want my bad behavior known in any manner, shape or form."

Bulger, 83, is accused of participating in 19 murders during the 1970s and '80s while he was allegedly leading the Winter Hill Hang and simultaneously providing information to the FBI on the New England Mafia and other criminals.

Connolly was convicted of tipping off Bulger to the 1995 indictment, prompting him to flee Boston in late 1994 and remain one of the nation's most wanted fugitives until his capture in Santa Monica, Calif., in 2011.

Morris acknowledged that he was concerned that he could potentially be prosecuted in the murder of Edward "Brian" Halloran, who prosecutors say was killed by Bulger after Connolly told Bulger that Halloran was cooperating with authorities against Bulger's gang.

Morris testified Thursday that he told Connolly about Halloran's cooperation. Another man, Michael Donahue, was killed during the same shooting because he happened to give Halloran a ride home that night.

Morris said he felt he had "no direct role" in the killings of Halloran and Donahue.

He said he agreed to cooperate with prosecutors because he "wanted to set things straight."

"I didn't want to carry that burden any more. I wanted to get out from under it," he said.

Morris acknowledged that there was pressure on FBI agents to cultivate informants who could provide information about the Mafia because bringing down the organized crime group was a top priority at the time.

Bulger attorney Hank Brennan repeatedly suggested that Connolly and Morris falsely portrayed Bulger as a top-echelon informant in the FBI's files so both of them could advance their careers. The defense maintains that Bulger bribed Morris, Connolly and others for information on investigations to help avoid prosecution, but say he was not an informant.

"The truth is, Mr. Morris, Mr. Bulger was buying, he wasn't selling, was he?" Brennan asked Morris.

"I didn't interpret it as a quid pro quo," Morris replied.

Brennan showed Morris two sets of reports on meetings with FBI informants, some purporting to be meetings with Bulger and some with other informants. In some of the reports, Connolly described information on gangland activities he attributed to someone other than Bulger. The same day or several days later, a report written by Connolly appeared in Bulger's FBI file, describing similar information.

"It's not real unusual that multiple informants can be reporting the same information," Morris said.

Brennan's cross-examination of Morris is expected to continue Monday.

Assistant U.S. Attorney Brian Kelly told Judge Denise Casper that Bulger's trial, which began earlier this month, is moving faster than anticipated. He said prosecutors could wrap up their case by the end of July, followed by the defense case.