A Pakistani officer says police have registered a case against unknown U.S. officials, seeking to press murder charges over a May 21 drone strike that killed Taliban leader Mullah Akhtar Mansour and a driver.

Abdul Wakil Mengal said Sunday police registered the case on behalf of the family of the driver, Mohammad Azam.

Azam's family says he is innocent, and was a sole breadwinner and father of four. They say they want justice.

The identity of the U.S. officials involved in the drone strike is unknown, and it is unclear if the charges will relate to those who ordered the attack or the U.S. servicemen who carried it out.

Azam's family may be seeking a trial in absentia and a symbolic victory or they may attempt to push for compensation.