Police are hunting for a man they say stole a wedding ring and backpack from one of the victims of the Portland train attack as he lay dying after being stabbed.

Ricky Best, a 53-year-old US military veteran who served in Afghanistan and Iraq, was allegedly murdered by Jeremy Joseph Christian, 35, after intervening to stop him racially abusing two women. Best and two other men confronted Christian when he began a race-hate tirade against two African-American women on the train, one of who was wearing a hijab.

Christian produced a knife and stabbed Best and 23-year-old student Taliesin Namkai-Meche to death. A third intervening man, Micah David-Cole Fletcher, 21, was slashed in the throat but survived.

Now police have released CCTV footage of a man leaving the same train in the aftermath of the fatal attack who they say may have stolen Best's backpack and wedding ring.

"The suspect is captured on surveillance video leaving the MAX train carrying Best's black backpack in his right hand," the Portland police department in the US state of Oregon said.

"The suspect is described as a white male with a blonde hair mullet, wearing a black Jordan Brand baseball cap, a black t-shirt featuring an image of Marilyn Monroe and an American flag, black shorts, and black shoes. The suspect carrying another backpack in his left hand, unknown if it his.

"Anyone with information on this suspect's identity is asked to provide it to Detective Mitch Hergert, mitchell.hergert@portlandoregon.gov."

Christian was charged with murder, attempted murder, possession of a weapon, and intimidation. In a court appearance, he ranted at the room: "You call it terrorism, I call it patriotism."

Portland train thief
The alleged thief of Ricky Best's items after he was killed in the Portland train attackPortland Police Bureau