One would think that by Jan. 28, 2014 -- the third time Joseph Johnson III had shot another human being -- he would have known how to handle a gun.

But the 40-year-old robber still apparently had a lot to learn about gun safety. Seconds after shooting his neighbor in the leg, he stuffed his .45-caliber semi-automatic handgun into the front of his pants and tried to run. He ended up shooting himself in the testicles.

Portland police had an easy time of finding Johnson, who was limping nearby.

Tuesday, Johnson, now 41, sat in a Multnomah County Circuit courtroom and asked a judge for leniency. He said he was “deeply ashamed” for his latest criminal episode -- wounding his neighbor during the course of a robbery in the parking lot of their downtown apartment complex.

Joseph Johnson III

Judge Youlee You, however, sentenced Johnson to 20 years in prison -- noting that his record of shooting others is “very troubling” and he poses a danger to society.

Johnson has spent 18 years of his adult life locked up. He had just finished serving a parole violation for drug possession and had been free for four months when he betrayed a friend, Jordan Merrell, the victim in his latest crime.

Merrell had met Johnson while in prison, and the two had even been cell mates. Merrell was was 15 in 1997 when during the course of a robbery he struck an 83-year-old Eugene man on the head, fracturing his skull and killing him.

Johnson also had twice been convicted of violent assaults -- shooting someone in San Francisco in 1994 and someone in Multnomah County in 2006 -- both over drug disputes.

Merrell was released from prison before Johnson. And when Johnson got out, Merrell helped Johnson get an apartment in his building, in the South Park Blocks near Portland State University.

On the evening of Jan. 28, Merrell and his wife were walking back home from Safeway with some ice cream when Johnson stepped out of the bushes with a gun, shot Merrell in the leg and began to run off with Merrell's wallet when he shot himself in the testicles.

“Mr. Merrell, to this day, is still wondering why this happened,” said deputy district attorney Jeff Auxier, who prosecuted the case. “He’s very confused.”

A jury found Johnson guilty of various counts, including first-degree robbery, second-degree assault and possession of methamphetamine. Merrell didn’t attend Tuesday’s sentencing hearing.

But Johnson’s defense attorney, DeAnna Horne, said Merrell and his wife have forgiven Johnson and still consider him a friend.

In asking the judge for leniency, Johnson acknowledged that he has problems, but that prison has done nothing to help.

“There’s something wrong with me that I can’t fix,” Johnson said.

-- Aimee Green