A former CIA contractor broke both agency rules and the law when he used a 2-foot-long metal flashlight to beat an Afghan man who later died, a prosecutor told a jury yesterday in the trial of the first American civilian charged with mistreating a detainee during the wars in Iraq and Afghanistan.

But lawyers for David Passaro said the former Special Forces medic was a frustrated but concerned interrogator who never hit Abdul Wali and checked daily on his condition.

“Dave is guilty only of trying to serve his country,” Mr. Passaro’s public defender, Joe Gilbert, said.

Mr. Passaro is charged with two counts of assault with a dangerous weapon and two counts of assault resulting in serious injury. Although Wali died in his cell, Mr. Passaro, 40, is not charged in his death. If convicted, he will face up to 40 years in prison.

Prosecutors told the jury yesterday that at least three paratroopers from the Army’s 82nd Airborne Division watched Mr. Passaro, working under contract to the CIA, beat Wali during two days of questioning in June 2003 about rocket attacks on a remote base housing American and Afghan troops.

The assistant U.S. attorney, Pat Sullivan, said Mr. Passaro told the soldiers they could not touch Wali but that he could “because I have special rules.”

Mr. Sullivan said Wali was chained to the floor and wall of a cell as Mr. Passaro kicked him and struck him. Once, he said, Mr. Passaro kicked Wali in the groin. But Mr. Gilbert told the jury that Mr. Passaro’s sole interest was to stop the rocket attacks, and once Wali surrendered, the attacks stopped. On the day Wali died, Mr. Gilbert said, Mr. Passaro gave him mouth-to-mouth resuscitation while other medics tried to help.