BAGHDAD, Iraq – The first forensic investigation into the murder by Saddam Hussein of hundreds of thousands of his people was made public yesterday after the excavation of a mass grave containing the bodies of blindfolded women, some with babies in their arms.

An American-led team has been secretly investigating a mass grave near the village of Hatra, in northern Iraq, where about 300 bodies have been found. Thousands more may be lying undiscovered.

The Iraqi government has identified 40 mass graves. But this is the first time that a proper study has been carried out because previous graves in the center and south of the country were generally excavated by distraught relatives determined to give the victims a decent burial.

The findings will be used by investigators for the Iraqi special tribunal that is seeking evidence to try Saddam and other leading Baath Party members for crimes against humanity.

In one grave investigators working for the tribunal found the bodies of pregnant women and children holding toys. Women had been blindfolded and shot in the back of the head. In another trench, men had been herded together and mown down by machine gun.

“This is a killing field,” said Greg Kehoe, an American lawyer working with the tribunal.

“One of the skeletons was of a little boy who was still holding a red and white plastic ball when we found him.”

Another body, photographed by the investigators, is that of a mother with her arm around her baby. The child was shot in the back of the head and the mother in the face. Some 120 bodies have been exhumed for forensic examination.

Investigators found two trenches outside Hatra containing 300 bodies believed to be of people killed in 1987 during the al-Anfal campaign in which Saddam removed ethnic Kurds from areas around the northern oilfields.

Many were forced south and thousands of others were massacred near their homes. Seven other trenches in the area have still to be opened.

Since July 5, investigators from the tribunal have been compiling evidence from documents seized after the fall of Saddam’s regime, as well as first-hand accounts and mass graves that have so far been unearthed.

Human rights groups say the former regime killed an estimated 250,000 Shia Muslims and 50,000 ethnic Kurds.

Mr. Kehoe has long experience of dealing with mass graves, including those that date from the vicious fighting in Bosnia in the early 1990s. But the difference is that in Bosnia the dead were usually men of fighting age, not women and children.

“You saw soldiers,” Mr. Kehoe said. “But two-year-old babies shot in the back of the head – I have never seen that before.”