Iraqi police say the handcuffed and blindfolded corpses of 10 unidentified young men were found in eastern Baghdad on September 19.
The police said they had been apparently killed by gunshots to the head.
It was not clear who was behind the killings.
Authorities say the corpses were recovered close to a disused pharmaceuticals plant near the Shi'ite district of Sadr City.
The men were aged between 17 and 25 and had been dead for up to two days.
It is the first time in several years that such a large number of bodies had been found in one place.
Summary executions were commonplace in Baghdad at the height of the Sunni-Shi'ite sectarian conflict in 2006 and 2007.
Based on reporting by Reuters and AFP