Pickett, who was 26-years-old when he was arrested on March 5, told authorities that he accidentally shot McGee at their Southeast D.C. home early in the morning of March 5.
At a preliminary hearing in the case, Detective Carter Adams testified that Pickett said he and McGee were arguing and he decided to stay the night elsewhere. While packing his belongings he picked up a gun and accidentally fired it when he was pushed or he tripped.
The bullet struck McGee in the shoulder, killing her, authorities said.
At his arraignment Thursday he was also charged with one count of possession of a firearm, to which he also pleaded innocent.
Judge Gerald Fisher set a trial date in the case for June 18. Pickett is expected in court Nov. 4 for a status hearing. He remains out of custody on personal recognizance.