KINGMAN, AZ - While Western New York native Timothy McVeigh set off the bomb that killed 168 people in Oklahoma City in 1995, he didn't act alone. And one of the key investigators is now talking about the probe all these years later.
Within 48 hours, the FBI made connections between McVeigh and an address in the city of Kingman, Arizona.
"When we did our homework on the Kingman address, we identified Michael and Lori Fortier," said FBI Special Agent Kenneth Williams, who was in charge of the Fortier investigation.
Michael Fortier served with McVeigh in the Army, and McVeigh was living with the Fortiers just a few months before the bombing.
"We sent a SWAT team up there. We sent a bunch of investigators initially," Williams said.
The FBI questioned Fortier for more than a dozen hours over several interviews, but his story remained the same: He had no idea his roommate was planning a terror attack.
Even though FBI officials believed Fortier, Williams thought he was hiding something.
"You get a gut feeling sometimes when you talk to a potential suspect," Williams said.
Slowly but surely, he found holes in Fortier's story. Search Warrants of Fortier's trailer eventually provided key evidence, including more than 100 detonators on his property.
Williams interviewed Fortier again, this time showing him photos of the bombing victims -- many children -- making an emotional appeal.
"He pushed away from the table and he said 'What about all the kids you guys killed in Waco, Texas?'" Williams recalled.
That's when it was clear Fortier was involved, but the extent was still unknown.
A semi-naked photo of Lori, Fortier's wife, was the final clue. The photographer was Timothy McVeigh.
Fortier asked Williams for a deal, offering to roll over on McVeigh.
The Fortiers may not have been in Oklahoma during the bombing, but they likely knew what would happen.
"He is just as responsible for the deaths of those people," Williams said.
Michael Fortier was sentenced to 12 years in federal prison. Lori Fortier received immunity.
Williams called their punishment "one of the biggest deals I've ever seen in my professional career."
While McVeigh got the death penalty and was executed in 2001, Fortier has been a free man since he was released from prison in 2006.
The bombing at the Alfred P. Murrah Federal Building in Oklahoma City remains the deadliest domestic terror attack in this country's history.