Army officials knew within days of Pat Tillman's (search) death that the former NFL player had been killed by fellow Rangers during a patrol in Afghanistan but did not inform his family and the public for weeks, The Washington Post reported.

A new Army report shows that Gen. John P. Abizaid (search), the theater commander in Afghanistan, and other top Army officials were aware an investigation had determined the death was caused by an act of "gross negligence" four days before a nationally televised memorial service, the Post reported after reviewing nearly 2,000 pages of documents it had obtained.

Tillman, 27, turned down a multimillion-dollar contract with the Arizona Cardinals (search) to join the Army after the Sept. 11, 2001, terrorist attacks. He was taking cover behind a boulder along a canyon road near the Pakistani border when a firefight erupted at twilight on April 22, 2004.

The Post reported on its online edition Tuesday night that troops on the scene said they were immediately sure Tillman was killed by a barrage of American bullets.

The documents show that officers erroneously reported that Tillman was killed by enemy fire, destroyed critical evidence and initially concealed the truth from his brother, also an Army Ranger, who was near the attack, the Post reported.

The memorial service in San Jose, Calif., took place May 3, 2004. The Army announced May 29 that Tillman likely died because of friendly fire.

Brig. Gen. Gary M. Jones (search), who prepared the report, concluded there was no official reluctance to report the truth.