(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's toys or items to indicate that minors were living in the house. The agent saw a shed but assumed it belonged to a neighbor.
"There was a deceptive false impression," Hinkle said. "If you were to be on the property walking around, you would have seen a big fence."
Parole Officers Carry Big Caseloads
Hinkle said the parole officer performed his duties appropriately. The parole officer was also responsible for raising suspicions when two University of California Berkeley officers notified him that Phillip Garrido came in with his "daughters." The parole officer called the Garridos in for questioning.
California has one of the highest parolee-to-officer ratios in the country. State budget cuts are expected to strain the department this year, which could mean reducing the number of parole officers, Hinkle said. The officer assigned to supervise Garrido was also responsible for 39 other sex offenders.
As recently as June, two months before Dugard was discovered with the Garridos, Contra Costa County firefighters responded to a fire on the property. They doused a car engine that had exploded into flames at the rear of the property, said department spokeswoman Emily Hopkins. They spent two hours there and then left.
They also visited Garrido's property in fall 2007, after a neighbor reported fire coming from the backyard. In addition, they responded twice in 2008 and three times in 2009 to medical emergencies involving Garrido's elderly mother, Patricia Franzen.
Fire department officials weren't sure whether more visits were made to the home, because computerized records date only to 2006.
Neighbors Steered Clear
Neighbors who had encounters with Garrido said they didn't take the time to get to know him. Some said they knew that he was a sex offender, so they steered away from his house. Others ignored him because they thought he was strange.
Betty Unpingco invited the entire neighborhood to her son's graduation party in spring 2006. She said Garrido attended and brought speakers for the party. When Unpingco and several adults noticed him talking to the high school girls, they asked him to leave. Later that night, she said, when they saw him waiting outside his home to speak to the girls, the adults escorted them home.
Feeling uneasy after the party, Unpingco checked the sex offender registry and found Garrido's picture.
"It was just so bizarre," said Unpingco, who has 10 children. "I warned my children to stay away from him and to always walk in twos." She did not notify police.
In November 2006, another neighbor did call police, saying she saw people living in tents behind the Garridos' house.
Contra Costa County Sheriff Warren E. Rupf said he didn't think the deputy who responded knew at the time that Garrido was a sex offender. The deputy spoke to Garrido in his front yard about the allegations, but Garrido convinced him otherwise.