BAGHDAD -- A suicide car bomb killed at least 21 people north of Iraq's capital yesterday, hours before Defense Secretary Robert M. Gates arrived to discuss with top commanders how many U.S. troops can be pulled from the country.
Meanwhile, a military jury convicted an Army sniper of murder and sentenced him to 10 years in prison for killing an Iraqi civilian who wandered into the hiding place where six soldiers were sleeping.
The bomber targeted an Iraqi police checkpoint at the entrance of a large open air-market in Balad, 50 miles north of Baghdad. Thirty-two people were injured, the U.S. military said.
"There were many bodies scattered, the smoke was dark, it was hard to see and it was dreadful," said Ali Jassim, a 34-year-old auto mechanic whose uncle was badly injured. "In my whole life, I haven't seen something like this."
According to an Iraqi military source, six of the dead were members of a U.S.-funded volunteer security force of Sunni fighters. Such forces, which include many former insurgents, have come under sharply increased attacks in recent weeks.
In Baghdad, Gates told reporters he would discuss troop levels with the top U.S. commander in Iraq, Gen. David Petraeus.
Petraeus is expected to testify before Congress in April about possible further cuts in American forces in Iraq if the decrease in violence seen late last year is sustained.
"I will obviously be interested in hearing from General Petraeus about his evaluation - where he stands and what more work he feels he needs to do before he's ready to come back with his recommendations," Gates said.
In the sniper case, Sgt. Evan Vela, 24, was found guilty of murder without premeditation, of aiding and abetting in planting an AK-47 on the dead man's body and of lying to military investigators about the shooting. He had faced a possible life sentence.
Vela showed no emotion when the verdict was read, but he asked the jury for mercy before it broke to decide his sentence. He apologized to the court, the Army and one of the sons of Genei Nasir al-Janabi, the man he shot with a pistol in May.
"When I came to Iraq, I didn't come to do anything wrong," Vela said, reading from a handwritten statement. "I failed my standards, your standards and the standards of the Army. All I can say is I'm sorry and ask for mercy."
Vela has been in confinement in Kuwait since July 1. That time will be credited to his sentence, the judge said. He also was sentenced to forfeit all pay and allowances and will receive a dishonorable discharge. The case was automatically referred to a military appeals court.
Vela's trial was the last for three snipers in the unit accused in a series of shooting deaths south of Baghdad that defense lawyers said happened under command pressure to increase kill counts and, perhaps, employ questionable tactics in doing so. The other two snipers were acquitted of murder charges.
In September, Gary Myers, then an attorney for Vela, claimed that Army snipers in Iraq were under orders to "bait" their targets with suspicious materials, such as detonation cords, and then kill whoever picked up the items.
The Army has declined to confirm that any such program existed, saying it does not discuss tactics used in the field.
While it does not appear the alleged baiting played in this case, James Culp, Vela's attorney, and others have argued the program may have encouraged the soldiers by blurring the legal lines in a complex war zone.
Vela and several of his fellow Army snipers testified that they were confused and exhausted after more than two days of trekking in high temperatures through rough terrain.
Also yesterday, U.S. forces investigating bombings this month at two pet markets in the capital raided Baghdad's primary hospital for the developmentally disabled and mentally ill. The military believes the bombings were carried out by two female suicide bombers who suffered from Down syndrome.
A man at the hospital was detained, but the military declined to identify him.
In the town of Fallujah, a car carrying a woman and young boy exploded yesterday, killing two police officers and injuring three other people, police said.
Garrett Therolf and Saif Hameed write for the Los Angeles Times. The Associated Press contributed to this article.