The lead investigator in a deadly bombing of Canadian troops in Afghanistan said U.S. pilots failed to follow procedure when they reacted to gunfire on the ground by dropping a bomb.

The April bombing, which killed four Canadian soldiers, showed a "reckless disregard" for standing orders, Air Force Brig. Gen. Stephen Sargeant testified Tuesday at a military hearing to determine whether the two pilots will face a court-hey spotted on the ground. They should have continued on their way rather than attacking, he said.

At an altitude of more than 15,000 feet, the pilots were not in range of the gunfire, said Sargeant, who was to be cross-examined again Wednesday.

"At that point it would have been possible to continue on," he said.

Defense lawyers asked the hearing officer, Col. Patrick Rosenow, to throw out Sargeant's testimony. They said the law bars the opinion of investigators on the cause of the accident from being considered as evidence in civil military proceedings.

Rosenow heard arguments on the issue, but did not immediately rule and allowed Sargeant to keep testifying. He said he would disregard the testimony if he concluded it was inadmissible.

Maj. Harry Schmidt, who dropped the bomb, and Maj. William Umbach, who was flying another F-16 and was mission commander, were charged with involuntary manslaughter and other counts after investigators concluded they had acted rashly by attacking in response to the ground fire. The gunfire came from live-ammunition exercises by the Canadian troops.

Defense lawyers have said the pilots fired in self-defense, unaware that allied troops were in the area. The lawyers placed some of the blame on poor military communication. They also suggested the pilots were pressured to take Air Force-issued amphetamines that impaired their judgment.

Earlier in the hearing, experienced F-16 pilots suggested the pilots were justified in attacking if they believed it was necessary to do so in self-defense. Prosecutors brought that up with Sargeant.

"Did you find this to be a rapidly unfolding situation?" Col. John Odom Jr. asked.

"No, in that there was nothing in the tapes that showed me a sense of urgency to force this situation rapidly drawing to the conclusion it did," Sargeant replied.

According to the general, Schmidt violated standing orders to keep himself out of danger by slowing his F-16 from about 500 mph to 400 mph and dropping his altitude to just over 10,000 feet.

"He could have just left," Sargeant said. "He should have accelerated out of this."

Instead, Schmidt dropped a 500-pound, laser-guided bomb on the Tarnak Farms firing range near Kandahar. Eight Canadians were wounded in addition to the fatalities, the nation's first in combat since the Korean War.

If convicted on all charges, which include aggravated assault and dereliction of duty, Schmidt and Umbach face up to 64 years in prison.