A U.S. soldier pleaded guilty Friday to killing a severely wounded Iraqi teenager in what investigators say may have been a mercy killing.

In a plea bargain, Staff Sgt. Johnny M. Horne Jr (search), 30, of Winston-Salem, N.C., pleaded guilty to one count of unpremeditated murder and one count of soliciting another soldier to commit unpremeditated murder under Articles 118 and 81 of the Uniform Code of Military Justice.

Horne had originally been charged with the more serious offenses of premeditated murder, conspiracy to commit murder and solicitation of another soldier to commit murder.

"He decided to plead guilty to the lesser charges presented to him," spokesman Lt. Col. James Hutton said.

The sentence, which may come Saturday, is solely at the jury's discretion. Had Horne been convicted of the more serious offensives, he could have faced life imprisonment or death.

Horne is among six Fort Riley (search) soldiers charged with killings in recent months — two for slayings in Kansas and four for deaths in Iraq. Staff Sgt. Cardenas J. Alban, 29, of Inglewood, Calif., is charged along with Horne in the teenager's killing and is awaiting a court-martial hearing.

The military tribunal heard witness testimony that troops fired on a group of Iraqi men placing homemade bombs along a road in Sadr City. Other soldiers arrived to find a burning truck and casualties around it.

Witnesses said the soldiers, including Horne, tried to rescue the teenager from inside the vehicle, but decided he was beyond help because of severe burns and abdominal wounds. A criminal investigator said the soldiers decided "the best course of action was to put (the victim) out of his misery."

Two other soldiers from the same unit this week faced Article 32 hearings — the military equivalent of a grand jury hearing — over a Sadr City killing in August.

An Article 32 hearing was held Thursday for Sgt. Michael P. Williams, 25, of Memphis, Tenn., on charges of premeditated murder, obstruction of justice and making a false official statement. Also charged is Spc. Brent May, 22, of Salem, Ohio, who had a two-day hearing and is awaiting a ruling on whether he will be court-martialed, receive a lesser penalty or be acquitted.

Horne's conviction comes almost a month after the Nov. 13 killing of another wounded Iraqi found lying in a Fallujah mosque among the bodies of several charges of murdering Iraqis during fighting in Baghdad's impoverished Sadr City (search) in August.

This week in Germany, a U.S. tank company commander was ordered court-martialed after being accused of shooting and killing a critically injured Iraqi driver for radical Shiite cleric Muqtada al-Sadr (search) on May 21 near Kufa, 100 miles south of Baghdad.

As in Horne's case, witnesses have said Capt. Rogelio Maynulet, 29, of Chicago, shot the wounded man out of compassion. Maynulet will be tried on charges of assault with intent to commit murder and dereliction of duty, which carry a maximum combined sentence of 20 1/2 years.

Human rights groups have condemned the illegal killings of Iraqis — either civilians or wounded fighters — by the U.S. military, saying such acts amount to violations of international humanitarian rights and should be dealt with as war crimes.

Critics also say poor understanding by young U.S. troops of the rules of military engagement leads to the killing of civilians.

"It doesn't help you win the hearts and minds of the public if you put a bullet in their hearts and another in the minds," said Mark Garlasco, senior military analyst for Human Rights Watch.

"There are a lot of 19-year-old troops out there with weapons who are very scared and are facing a concealed enemy who is attacking them while not following any international standards of warfare," Garlasco said. "This doesn't excuse them, but it shows there is a level of understanding."

Another human rights group, London-based Amnesty International, said killings like the one in Fallujah must be treated as war crimes and the perpetrators brought to justice.

"A wounded person who doesn't pose a threat to the other side should not be killed, they are no longer a combatant," said Amnesty's Middle East program director, Abdul Salam Sid Ahmed.

The U.S. military has defended its record, saying out of the more than 400,000 soldiers who have deployed to Iraq since the war began, only a few illegal killings have come to light.

Lt. Col. Steve Boylan, a spokesman with the military command in Baghdad, said soldiers understand the rules of engagement and go through extensive training.

"The U.S. military is a cross-section of the U.S. society, where we have the complete spectrum of best possible people that you could imagine, but unfortunately we have those at the other end who commit crimes and they are held accountable," he said.

Meanwhile, the U.S. command said two soldiers died Thursday and four were injured when an AH-64 Apache helicopter crashed into a UH-60 Black Hawk chopper that was on the ground at an airfield in the northern city of Mosul. A U.S. Marine was also killed in action in volatile Anbar province west of Baghdad.