Sept. 11, 2009 -- Ever since he was a kid, Kevin Tillman was never far from his big brother, Pat.
On April 22, 2002, both were Army Rangers, and Spc. Kevin Tillman pulled up to the scene of his brother's shooting manning a turret gun on a Humvee just minutes after Pat Tillman was slain in a hail of friendly fire.
"What's going on?" Kevin Tillman asked his fellow Rangers, having heard the shooting as his vehicle struggled through a rocky, narrow Afghan canyon that kept its speed below 5 mph.
When a Ranger asked the driver of Kevin Tillman's vehicle if the crew had a litter for carrying casualties, Tillman asked, "Who got hit?" He was told it was an Afghan.
An Afghan had been killed alongside Pat Tillman.
Watch the story tonight on "Nightline" at 11:35 p.m. ET and watch best-selling author Jon Krakauer's first live interview about his new book "Where Men Win Glory: The Odyssey of Pat Tillman" Monday on "Good Morning America."
While standing guard, Kevin Tillman said he became uneasy because his brother's booming voice and laugh was missing from the scene.
"I started to get a little weird feeling, you know, because my brother's a pretty loud-type guy," Kevin Tillman told an investigator who looked into the friendly fire incident.
"Where's Pat?" he began asking his colleagues.
"He asked me three times," said Sgt. Jason Parsons.
Finally, the sergeant told Kevin Tillman that his brother was dead.
Tillman was silent for a few minutes. Then he howled and cursed in grief and rage. The platoon's doctor took his gun away.
But even though it was apparent to most of the platoon members who were present for the shooting's aftermath that Pat Tillman had been killed by a fellow Ranger, no one told Kevin Tillman.
Later that night, Kevin Tillman was summoned by Maj. David Hodne as Tillman got off a helicopter that evacuated him from the shooting site to offer Tillman a chance to be counseled by a chaplain. Tillman declined the offer, and asked Hodne for a promise instead.
"He asked me to promise to exact revenge on the ambushers," Hodne testified to an Army investigator, according to Krakauer.
Hodne said he promised that whoever killed Pat Tillman would pay dearly, a vow that Krakauer said was the Army's first lie to the Tillman family.
Kevin Tillman was born 14 months after Pat Tillman, and because his older brother pronounced "Kevin" as "Nubbin," the name Nubbin or Nub has stuck with Kevin throughout his life.
While Pat Tillman played professional football, Kevin Tillman was signed by the Cleveland Indians and played professional baseball in the Indians' minor league system.
When Pat Tillman decided to enlist, his wife Marie remembered telling him, "It's not fair to Kevin, in some ways -- because you know he's going to come with you."
The two Tillmans went through the Army's boot camp together and later the grueling Ranger school. They were both deployed to Iraq and then sent to Afghanistan together. In their off hours, Kevin Tillman lived with Pat and Marie Tillman.
Ranger Ordered to Keep Friendly Fire Secret From Kevin Tillman
Kevin Tillman accompanied his brother's body back to the States, but on the day he left he asked nearly every Ranger he met to find the notebook that his brother was carrying to jot down his thoughts. All assured Kevin Tillman they would look for it.
Instead, the notebook was burned along with Pat Tillman's uniform and body armor.
Desperate to hear firsthand how his brother died, Kevin Tillman repeatedly called his unit in Afghanistan trying to reach Pfc. Bryan O'Neal, the youngest Ranger in the platoon who was with Pat Tillman when he died.
Tillman called eight times before someone agreed to allow O'Neal to talk on the phone, but O'Neal was ordered to keep the friendly fire a secret from Kevin.
"I was appalled that when I was able to actually speak with Kevin, I was ordered not to tell him what happened," O'Neal testified, according to the book.
When the unit returned to the United States, Kevin Tillman was there to greet them and in the ensuing days even worked out with some of the soldiers who had fired on his brother. No one mentioned to Tillman what really had happened back on that Afghan mountain.
Later that day, a senior officer realized the secret couldn't be kept from Tillman forever, and called him in to tell him the truth. The news stunned Tillman. He also was stunned at how casually his comrades had kept the news from him, including those who had killed his brother.
"I did my PT [physical therapy] with two of the people who killed Pat and then went to breakfast with the P.L. [platoon leader] who eventually got fired, telling him, 'Hey, you did a good job out there,' not having a clue what really went on," Kevin Tillman later testified at one of the seven investigations into his brother's death.
Kevin Tillman asked Congress for an investigation into his brother's death because he no longer trusted the generals he served under.
Recapping the string of lies and official reports that called the military's actions "missteps," Kevin Tillman testified, "These are intentional falsehoods that meet the legal definition of fraud. ... These are deliberate acts of deceit."
Despite the betrayal by the Army, Kevin Tillman decided to finish out his enlistment and remained in the Army until July 2005.
In 2008, he published a book about the Iraq war entitled, "The Transparent Pillage."