The conviction was questionable to begin with.
Via Daily Caller:
President Donald Trump issued a full pardon Monday to former Army First Lieutenant Michael Behenna, who served five years in prison after being convicted of murdering a suspected Al-Qaeda terrorist.
In May 2008, Behenna was questioning Ali Mansur Mohamed, a suspected terrorist who had allegedly been involved in an IED attack that killed two U.S. soldiers. The interrogation ended when Behenna fired two rounds into the terrorist — which the 1st Lt. claimed was in self-defense after Mansur lunged for his pistol.
A military court convicted Behenna of unpremeditated murder in a combat zone in 2009. The prosecution said Behenna was not acting in self-defense, but in retaliation for the deaths of his fellow soldiers, and killed Mansur while returning him to his hometown.