George Tschaggeny, 51, was wearing Best's ring when he was arrested at a small homeless camp under a Portland overpass, Simpson said.
Tschaggeny faces three charges, including theft in the second degree, tampering with physical evidence and abuse of a corpse in the second degree.
Best, 53, and Taliesin Myrddin Namkai-Meche, 23,
suffered fatal stab wounds May 26 on the MAX train in Portland while intervening to stop a man yelling anti-Muslim slurs at two teenage girls. The stabbings attracted widespread national attention.
Jeremy Joseph Christian
, 35, the man suspected in the stabbings, was arrested shortly after leaving the train.
Video evidence from the stabbings "supports the charges" of Tschaggeny removing Best's ring, Simpson said. Best died at the scene, police have said.
Best's camouflage, military-style wallet remains missing, the police spokesman said.
"It's completely heartless. There's no other way to describe what happened," Simpson said. "That action is just incredibly heartless and unconscionable."
Appeal for help
Portland police had appealed to the public for help in locating the suspect in the theft of Best's backpack and wedding band.
The department released surveillance video showing the theft suspect departing from the train after the stabbings.
In the video, he is carrying what authorities said is Best's black backpack in his right hand and another backpack in his left hand.
Police described the suspect as a white male with a blond hair mullet who was wearing a black Jordan Brand baseball cap, black T-shirt with an image of Marilyn Monroe, black shorts and black shoes.
It's unclear whether the backpack in the man's left hand belongs to him, police said.
Man arrested in the killings
After boarding the MAX light rail train last Friday afternoon, Christian went on a tirade directed at two African-American teenagers -- one who was wearing a traditional Muslim hijab, according to witnesses and a police affidavit. Police said the attacker slashed the throats of Best and Namkai-Meche, as they tried to defend the girls, killing them. A third man, Micah Fletcher,
21, was seriously injured and has been hailed as a hero.
Once arrested, Christian made shocking statements when he was put in the back of a police car equipped with audio and video recording devices, according to an affidavit released Tuesday.
"I stabbed the two (expletives) in the neck and I'm happy now," he was recorded as saying. "I hope they all die. I'm gonna say that on the stand."
Stabbing suspect faces 9 charges
Christian faces nine charges: two counts of aggravated murder, attempted aggravated murder, first-degree assault, three counts of unlawful use of a weapon and two counts of intimidation.
The aggravated murder charges carry a maximum penalty of death. Oregon has not executed a prisoner in more than two decades.
CNN has reached out to Christian's attorney for comment.