Ten years ago in Oklahoma City, small pieces of debris from the Alfred P. Murrah Federal Building bombing yielded big results.
The bits and pieces ultimately led to the arrests and eventual convictions of Timothy McVeigh (search) and Terry Nichols (search). When the Murrah building was bombed on April 19, 1995, it killed 168 people and left a large swath of debris in downtown Oklahoma City.
Now, two former FBI agents who helped solve the case have written a book detailing the investigation. Jon Hersley (search) and Larry Tongate (search) wrote "Simple Truths" to show Americans how the evidence trickled in and the case was solved.
"I had lived in Oklahoma City for 20 years. ... I wanted very much to find out who was responsible for this crime," Hersley said.
Hersley recalls locating the rear axle of the Ryder rental truck that was used in the attack and being able to trace the partial vehicle identification number, which led investigators to a body shop in Kansas where the truck was rented.
Records from Elliott's Body Shop showed the truck had been signed out by Robert Kling, which was also found on a receipt for Chinese takeout that was delivered to a motel where witnesses described seeing a parked Ryder truck.
But when investigators went to the Dreamland Motel to follow up on the lead, the clerk told them the man with the truck had registered under the name Timothy McVeigh. It was the first mention of the name that would lead investigators to their prime suspect.
"That's when it all started, that's when the big FBI machine starts to grind really fast. And an ATF [Alcohol, Tobacco and Firearms] agent, to his credit, did a ... check and found out that a Tim McVeigh had been arrested in Perry, Oklahoma, and he was in custody and that was ... the break of the century," said retired FBI agent Danny Coulson (search).
After parking the Ryder truck in front of the Murrah building the day of the bombing, McVeigh fled the scene in a getaway car and was en route to see co-conspirator Nichols when he was pulled over by an Oklahoma State Trooper for driving a vehicle without license plates.
When Trooper Charlie Hanger approached the car he saw McVeigh had a firearm on him, which turned out to be unregistered. Hanger arrested the man and put him in jail. Authorities were able to find McVeigh was in jail just in time.
"He was probably within 15 or 20 minutes of being bonded out. He was in [the] process of appearing before the judge. He was really close to getting out of jail," Hanger recalled.
As McVeigh was sitting in a Perry, Okla., jail cell, Terry Nichols was in his Kansas home, waiting to hear from his partner in crime. When McVeigh failed to contact him, Nichols panicked, according to the FBI agents.
Tongate said a person visiting one of Nichols' neighbors reported seeing the co-conspirator spreading ammonia nitrate fertilizer on his yard and said it looked like it was snowing.
Nichols drove to police in Herington, Kan., and began talking to agents, giving them some half-truths and some outright lies.
Nichols feared that his vehicle might have been spotted as it cased Oklahoma City, two days before the bombing. A surveillance camera at the Regency Towers Apartments proved to be a valuable tool for the FBI.
Hersley said agents were able to identify Nichols' pickup truck circling the area a few nights before the bombing.
When agents searched Nichols' home they found more evidence linking him and McVeigh to the bombing, including a drill and drill bit used to break into a quarry, where large amounts of explosives were stolen.
In the kitchen they found a receipt for 2,000 pounds of ammonium nitrate fertilizer, which was purchased by Mike Havens, an alias used by Nichols.
A key piece of evidence was the payment book for a telephone calling card, which investigators found had been used to make 685 calls between the two men. The address from where payments were repeatedly made was the Nichols' family farm in Michigan.
"We know from the use of the ... calling card that there was a great deal of effort ... trying to obtain the racing fuel — the liquid component of the bomb — sold at race tracks, and that's why they went down to Ennis, Texas, and they purchased three 55-gallon barrels of racing fuel," Hersley said.
Another big tip was from Sgt. Richard Wall, who called the FBI to say he had observed a Ryder truck at Geary Lake on April 18 and near it was parked a truck similar to the one driven by Nichols.
But 10 years later, Coulson believes we still don't know everything there is to know about the bombing.
"I think there's unanswered questions that need to be answered, and it would be good for the American public to have these answers," Coulson said. "I think some of the answers lie in the files of the FBI and ATF."
FOX News' Rita Cosby, Clay Rawson and Peter Russo contributed to this report.