BAGHDAD, Iraq (CNN) -- U.S. soldiers investigating a shooting by Blackwater guards that left 17 Iraqis dead found no evidence the security contractors were fired upon, a source familiar with a preliminary U.S. military report said Friday.
A man bicycles past a car on September 20 that was damaged during the September 16 Blackwater shootings.
The soldiers also found evidence suggesting the guards fired on cars that were trying to leave Nusoor Square in Baghdad during the shootings, the military source said.
The report said the weapons casings found by soldiers, who arrived about 20 minutes after the shooting subsided, matched only those used by U.S. military and contractors, the source said.
The soldiers "did not find any cartridge casings that would have matched those used by Iraqi security forces or insurgents," the source said.
Blackwater has no comment on the report, spokesman Anne Tyrell said.
Lt. Col. Mike Tarsa commands the 3rd Battalion, 92nd Field Artillery Regiment of the 2nd Brigade, 1st Cavalry Division. His unit conducts patrols in the Nusoor Square neighborhood of Baghdad, the U.S. military source told CNN.
The unit was first to arrive at the scene, and soldiers took witness statements, photographs, and made assessments.
The source confirmed remarks made by Tarsa that were reported Friday in The Washington Post.
"It appeared to me they were fleeing the scene when they were engaged. It had every indication of an excessive shooting," Tarsa is quoted as saying.
"I did not see anything that indicated they [Blackwater guards] were fired upon."
Maj. Winfield Danielson, a U.S. military spokesman in Baghdad, said the military is conducting an inquiry because the incident took place "in our battle space," and because the military wants to "see what we can learn from it to apply to our contractors." He said the military has about 40 private security contractors.
The September 16 shootings involved Blackwater security contractors guarding a State Department convoy.
Iraqi officials say Blackwater guards indiscriminately opened fire, killing civilians. A senior Iraqi national police officer said 17 people were killed and 27 wounded, all of them civilians except for one traffic police officer, who was wounded.
Blackwater has said its contractors "acted lawfully and appropriately in response to a hostile attack," and "the 'civilians' reportedly fired upon by Blackwater professionals were in fact armed enemies, and Blackwater personnel returned defensive fire."
The U.S. State Department has said that "innocent life was lost."
The FBI, representing the U.S., and the Iraqis are conducting a joint investigation.
Earlier this month, a senior Iraqi National Police officer showed CNN an Iraqi police report on the events of September 16.
That report contains some similar information. It says that, according to witnesses, Blackwater guards fired on people fleeing the scene. And it says the guards did not come under fire, the Iraqi officer told CNN.
North Carolina-based Blackwater has worked in Iraq since the U.S. invasion in March 2003 and has received more than $1 billion in U.S. government contracts, including $832 million to protect State Department officials, since 2004, according to a U.S. congressional staff report.
On Thursday, a Philadelphia law firm filed suit against Blackwater on behalf of families of those killed or wounded in the square, calling it a "summary execution."
Also Thursday, military officials in Iraq said weapons belonging to three U.S. soldiers -- two dead and one missing after an attack in May -- turned up in a house raid this week.
Two U.S. M-4s, one M-203 grenade launcher and an M-249 squad automatic weapon belonging to the soldiers were among other weapons and explosives found Tuesday in a house south of Baghdad, according to a statement issued by Multi-National Corps-Iraq.
Officials matched the serial numbers of the weapons with the soldiers, the statement said.
The weapons belonged to Spc. Alex Jimenez Jr., Sgt. Anthony Schoeber and Pfc. Joseph J. Anzack Jr. Their military observation post outside Mahmoudiya, south of Baghdad, was attacked by insurgents on May 12.
Schoeber was killed in the attack, and Anzack's body was pulled from the Euphrates River 11 days later.
Jimenez and another soldier, Pvt. Byron Fouty, have been missing since the attack. In June, coalition forces found Jimenez and Fouty's identification cards in a raid on a suspected al Qaeda in Iraq safe house, about 90 miles north of the site of the attack. The U.S. military classified the two as missing-captured.
Nine Iraqis were detained during Tuesday's house raid and are being held for questioning, the military said. Officials could not say if any of the detainees had information about the missing U.S. soldiers.
Meanwhile, a security official in Iraq's Salaheddin province says a U.S. military operation Thursday night killed 20 civilians, most of them women and children.
The U.S. military estimated Thursday that 15 civilians were killed by coalition forces in the operation targeting senior leaders of al Qaeda in Iraq.
The military said the terrorist group put the victims in harm's way.
The U.S. military said Thursday its attack in the Lake Thar Thar region killed 19 suspected terrorists and 15 civilians, six of them women and nine children. The military said another six people were wounded: two suspects, one woman, and three children. One suspect was detained. E-mail to a friend
CNN's Jennifer Deaton, Jomana Karadsheh and Ingrid Formanek contributed to this report.