(CNN) -- A Philadelphia law firm filed suit against Blackwater USA on Thursday on behalf of the families of Iraqis killed and injured in last month's shooting in Baghdad's Nusoor Square. In this September 24 photo, an Iraqi looks at a car that was destroyed during the September 16 incident. The suit calls the incident a "senseless slaying" and claims it was part of "Blackwater's lengthy pattern of egregious misconduct in Iraq." "This was a summary execution, an execution without a trial," said Michael Ratner, president of the Center for Constitutional Rights which is part of the legal team. The September 16 shooting in western Baghdad left 17 Iraqis dead, according to Iraqi officials who called the incident "premeditated murder" in a report released this month.
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Federal suit filed in Washington on behalf of slain and injured Iraqis
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Suit: September shooting a "senseless slaying" and part of a "pattern"
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Blackwater has maintained that it acted "acted lawfully and appropriately"
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Iraqi officials say 17 were killed in Baghdad's Nusoor Square on September 16
But the @placeholder shootings have put contractors' role in the 4-year-old war under new scrutiny.