(CNN) -- More than two dozen times in the past three years, authorities came to Phillip and Nancy Garrido's ramshackle home at 1554 Walnut Ave. in Antioch, California, a rural property where Jaycee Dugard is said to have been confined for 18 years.



Jaycee Dugard was locked in a shed tucked under a blue tarp in her alleged captor's backyard.



And each time, they left without learning of the secret shed where Dugard lived.



The Garridos have pleaded not guilty to charges of abduction and forcible rape. They are being held without bail in the Contra Costa County Jail in Martinez, California.



After she was abducted in June 1991, at age 11, Dugard's disappearance spawned a massive search that continued, on and off, for almost two decades. Federal agents remained committed to the case, chasing thousands of leads.



But they apparently never had the Garridos on their radar.



The case of the missing girl evoked deep emotions that rippled across the South Lake Tahoe community. Strangers threw fundraisers and parades to raise money for search efforts. Friends and neighbors wore T-shirts bearing images of Dugard's smiling face to give the case exposure. Elementary school students toted signs that encouraged the community to stay committed to the hunt for their classmate.



All they wanted was to find little Jaycee Lee Dugard.



And for some of that time, authorities were visiting the home of the couple now accused of abducting her.  Watch an FBI agent talk about why clues were missed »



Interviews with public officials show that parole officers, law enforcement officials and firefighters visited the Garrido household but left without realizing that the kidnapped girl had grown to adulthood and was living in a soundproof shed hidden in the backyard.



Two Dozen Contacts



There were at least 16 visits from parole officers and seven by the fire department. There was also one by the sheriff's office responding to an allegation that people were living in the backyard. State and local authorities have now begun internal investigations to find out why none of these visits uncovered the existence of Dugard, now 29, and her children, Starlet, 15, and Angel, 11.



Their makeshift home of tents, tarps and sheds was tucked behind a 6-foot wall at the rear of the Garrido property.



"I feel confident the sheriff will use this as an example of how to do things better," said Federal Glover, a district supervisor for Contra Costa County who also heads the community's public safety committee. "From this lesson, we will not have this type of missed opportunity occur again."



One of the first red flags authorities might have caught was in 1993, two years after the kidnapping.



Garrido, who had been released from prison after serving 11 years for a 1976 kidnapping, violated his parole in April 1993. It is unclear what he did or how the violation was flagged. As a result, he was placed in federal prison for one month and then released on house arrest for three months. He returned to the Antioch home, where he lived with his wife and his elderly mother.



Violation Wasn't Reported to Nevada



But the parole violation was never reported to the state of Nevada, where the first kidnapping and rape had occurred, said Gail Powell, a spokeswoman for the Nevada Department of Public Safety.



"The state of Nevada would have taken some action," Powell said. "I don't know what, but some action could have meant putting him back in prison, pulling him off parole."



In 1999, the California Department of Rehabilitation and Corrections agreed to take responsibility and authority for supervising Garrido's parole because he resided in that state.



Garrido's most recent parole agent visited the home at least twice a month since December, according to California corrections officials. Sometimes the visits were unannounced, said Gordon Hinkle, a department spokesman.



Parole officers also checked on Garrido frequently before 2008, Hinkle said, but he did not know how often or how many parole officers visited Garrido's residence.



The parole agent who most recently entered Garrido's backyard didn't notice any children
Officials visited Garrido home more than two dozen times in? Who did police visit? Garrido violated? Who checked up on Garrido at least twice a month? Who did officials visit? Phillip Garrido's parole officer checked up on him at least? What number of times did they visit? Garrido's parole officer checked on him how often? How many times have officials visited Garrido home in the past three years? Garrido's parole officer checked up on him how many times per month? When did Garrido violate parole? What year did he violate parole? When did Garrido violate his parole? Official have visited Garrido home more than two dozen times in the past how many years?
the past three years, the Garrido household his parole most recent parole agent Phillip and Nancy Garrido's twice a month than two dozen than two dozen times than two dozen than two dozen April 1993. 1993. April 1993. three
question: Officials visited Garrido home more than two dozen times in?, answer: the past three years, | question: Who did police visit?, answer: the Garrido household | question: Garrido violated?, answer: his parole | question: Who checked up on Garrido at least twice a month?, answer: most recent parole agent | question: Who did officials visit?, answer: Phillip and Nancy Garrido's | question: Phillip Garrido's parole officer checked up on him at least?, answer: twice a month | question: What number of times did they visit?, answer: than two dozen | question: Garrido's parole officer checked on him how often?, answer: than two dozen times | question: How many times have officials visited Garrido home in the past three years?, answer: than two dozen | question: Garrido's parole officer checked up on him how many times per month?, answer: than two dozen | question: When did Garrido violate parole?, answer: April 1993. | question: What year did he violate parole?, answer: 1993. | question: When did Garrido violate his parole?, answer: April 1993. | question: Official have visited Garrido home more than two dozen times in the past how many years?, answer: three