A federal appeals court has concluded that a 28-year prison sentence is too lenient for a Libyan militant who was convicted of terrorism-related charges in the 2012 attacks on U.S. compounds in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans.

The motion in Washington's federal court does not detail the newly disclosed evidence but says it concerns a key government witness who testified under the pseudonym Ali Majrisi at Khattala's 2017 trial. Khattala was captured in 2014 and put on trial for an attack that became a divisive political flashpoint during the tenure of former Secretary of State Hillary Clinton. A jury convicted Khattala of multiple terrorism-related charges but found him not guilty of murder. Prosecutors accused Khattala of heading an extremist militia and directing the attack but acknowledged that they lacked evidence of him firing any weapons. The motion for a new trial comes just before the three-year anniversary of the guilty verdict, the deadline under federal rules of criminal procedure for such a request.