June 4, 2008 -- As soon as she met Scott Kimball, Mary Willis says she felt chilling suspicion: Kimball, the man who was supposed to help the FBI solve her daughter's disappearance, was the one who had killed her.
Kimball had negotiated an early release from prison in late 2002, a few months before 25-year-old Jennifer Marcum disappeared, to work as an FBI informant. He'd told officials he had information about an alleged murder plot Marcum and her boyfriend were planning.
But after meeting the charming ex-con in the summer of 2005, Willis quickly became suspicious. "He went into detail about how she died, where the body was," she said. "He was smug about it. He told me a lot of terrible things."
Willis said she told the FBI she believed Kimball was involved in her daughter's death, but she said the bureau told her the case was under control.
"You tell me how as soon as that information is given to the FBI they still didn't do anything. They didn't take him in," she said. "He's more or less saying, 'I killed her' and laughing in their faces."
The FBI now believes Kimball may have been involved in the disappearances of at least three people, including Marcum and the death of his ex-wife's daughter. An FBI spokeswoman in Denver declined to comment on the specifics of the case.
Kimball's role as an informant, disclosed in a federal search warrant, has outraged some of the parents of the missing women.
"I believe Kaysi would not be gone if it weren't for" the FBI, said Lori McLeod, one of Kimball's ex-wives, whose daughter Kaysi's body was discovered earlier this year. "I believe that she is dead because of the FBI. They don't monitor their informants, they literally let them out and they run amok."
Kimball is in a Colorado jail on unrelated weapons and fraud charges, and has not been charged in connection with the death or disappearances. His lawyer did not return a message seeking comment.
At the same time, McLeod said she appreciated the bureau's current efforts to solve her daughter's death. The McLeods learned in April that Kayci's remains were found in the woods in northern Colorado. Her father, Rob McLeod, also praised the bureau's work.
"As soon as we got on board they've been 100 percent cooperative," he said. "I hold Scott Kimball responsible for his actions."
It's unclear how much the FBI knew about Kimball when it agreed in late 2002 to his release as an informant. The U.S. Attorney's Office in Denver also asked a judge to allow Kimball to work as a cooperating witness for the FBI, according to a law enforcement official who spoke on the condition of anonymity.
Kimball's case is not the first time the FBI has been accused of mishandling an informant. In 1995, FBI agent John Connolly famously tipped off Boston mobster and informant James "Whitey" Bulger of a pending federal indictment, allowing him to escape. Connolly was convicted in 2002 for his role in the case. No FBI agents have been accused of misconduct in the Kimball case.
In a 2005 review of 120 informant files, the Justice Department's inspector general found that FBI agents violated internal guidelines in 87 percent of the cases, including some in which informants allegedly engaged in illegal activity without proper oversight or permission.
"These guys are criminals. That's why you come into contact with them in the first place. They're evil people," said Joe O'Brien, the former FBI informant coordinator in New York City, who was not familiar with the Kimball case.
"I don't know that anything necessarily could have been done to prevent what happened" in the Kimball case, he said.
Before his release in December 2002, Kimball had a record that included crimes such as forgery and issuing bad checks, but according to court records, he had never been convicted of a violent crime.
In 1999, Kimball's ex-wife accused him of breaking into her home, binding her and repeatedly raping her, according to a federal search warrant affidavit. Kimball was never charged in relation to those accusations.
According to the affidavit, Kimball told police in Spokane at the time that he was a cooperating witness and that sex with his ex-wife was consensual. Spokane police spokeswoman Teresa Fuller said investigators had no recollection of Kimball saying he worked as an informant and that there was "nothing to substantiate" his ex-wife's claim.
It was unclear if Kimball was in fact working as an informant at the time or if the FBI was aware of the rape accusations against Kimball when he was released from prison. Both the FBI and U.S. Attorney's Office in Denver declined to comment.
Kimball persuaded federal law enforcement officials to let him out of prison in December 2002, saying he had information that Marcum and her boyfriend were hatching a murder-for-hire scheme to kill an associate.
Over at least the next 18 months, Kimball gave information to the FBI -- apparently attempting to blame Marcum's disappearance on others, according to the affidavit.
"The only thing I can say is the guy is very convincing and manipulative," said Detective Gary Thatcher, who investigated Kimball for the Lafayette, Colo., police department. "He's a very unique suspect. It's not hard to see how he would have duped even law enforcement."
The FBI said Kimball was not on its payroll but was paid only when he brought valuable information to the bureau. Another of Kimball's ex-wives, Lori McLeod, said the FBI paid Kimball about $4,500 a month and at one point gave him a $20,000 bonus.
McLeod told ABC News that she met Kimball's handler at the FBI and dropped Kimball at the FBI offices several times. "All of these girls were being killed while he was getting money from the FBI," she said.
Marcum disappeared Feb. 17, 2003, less than two months after Kimball left prison. Kaysi McLeod, 19, was last seen Aug. 23, 2003.
Both women had troubled pasts, and their disappearances apparently raised few questions among law enforcement officials. It wasn't until their fathers realized that the last person to see both women alive was Kimball and contacted the FBI that the cases were investigated in earnest.
After Marcum's car was found at the Denver airport the day after she was last seen, Kimball claimed that she bought a gun for $600 and headed to New York as part of the supposed murder-for-hire plot, the affidavit alleges. There is no evidence, however, that Marcum ever got on a plane.
Kimball later changed his story and told authorities that Marcum had been killed by one of her boyfriend's associates, the affidavit says. Kimball told authorities that he had been asked by the associate to dig up Marcum's body and rebury her because he was afraid she could be identified by her breast implants and IUD.
When asked in July 2003 why both his and Marcum's cell phones weren't being used between Feb. 17 and 20, 2003 -- the days after Marcum was last seen -- Kimball told the FBI that he had been on a trip to the mountains and his cell phone had been off, according to the affidavit.
Kimball was arrested in March 2006 in California after fleeing a Colorado arrest warrant for fraud. The current FBI case agent was assigned to Marcum's case in November 2006.
When she met Kimball in August 2005, Willis claims Kimball told her that her daughter was strangled, and that she put up a fight before she died.
"He told me he wanted to show me how she died," she said and asked her to send her other daughter so Kimball could demonstrate Marcum's death on her.
Marcum's father, Bob, said Kimball insisted that he knew where Jennifer's body was and wanted to give her a "good Christian burial." But Bob Marcum did not trust Kimball to show him the grave.
"I figured he was a killer, and I wasn't going anywhere with him. I figured I'd end up dead after the things that he said," Bob Marcum told ABC News.
ABC News' Andrea Beaumont contributed to this story.