The suspect under investigation following the fatal shooting of a Patriot Prayer supporter has been named as a father-of-two who describes himself as '100% ANTIFA' and was previously cited for bringing a loaded gun to a different protest.

Michael Forest Reinoehl, 48, was named by The Oregonian Sunday evening as someone police are investigating. He had already been accused of taking a loaded gun to an earlier Portland protest and social media posts show him attending Black Lives Matter protests. 

Reinoehl has not been charged nor have police commented on his connection to Saturday night's violence but his relatives also told the local newspaper that he was the person in a video of running away from where Aaron Jay Danielson, a supporter of the right-wing group Patriot Prayer, had been shot dead.

President Trump retweeted the victim's name and wrote, 'Rest in peace Jay!' afterwards. On Monday morning, he also threatened to send in the National Guard. 

'Portland is a mess, and it has been for many years. If this joke of a mayor doesn't clean it up, we will go in and do it for them!' he wrote.

Reinoehl is said to be estranged from his most of his family, with his sister telling the paper: 'We reached out to police and confirmed that we recognized Michael in the screenshots [from the incident]. 

'On the one hand, this whole thing surprises the daylights out of us, because we always thought he is a lot of bark, not a lot of bite. But he's also been very impulsive and irrational.'