Billy A. Moore, 17, died Monday evening at his home in a North Portland housing project, shortly after he was shot after exiting the city bus near a Boys & Girls Club, police said.

PORTLAND — A Portland teenager was fatally shot following an argument on a bus ride home from a visit with his dying mother, and a 16-year-old has been charged with his murder, authorities said Tuesday.

Billy A. Moore, 17, died Monday evening at his home in a North Portland housing project, shortly after he was shot after exiting the city bus near a Boys & Girls Club, police said.

The suspect was arrested Tuesday morning and was being held at a juvenile detention center. Detective Mary Wheat, a Portland police spokeswoman, said the boy's name would likely be released Wednesday.

Moore died hours before his mother, 44-year-old Valerie Martinez, succumbed to leukemia at OHSU hospital. An uncle, Richard Villalobos, said the family learned of the shooting while at the hospital, awaiting the hour when the woman would be removed from life support.

According to witnesses, after Moore was shot in the back, he ran about a block and a half to his home, spilling blood on the street and sidewalk. He barged in the front door and went out to the backyard.

Neighbor Gabriel Hardy, 28, said he heard multiple gunshots before seeing Moore in the yard. The teenager was bleeding from the mouth, barely able to speak.

Hardy said he squeezed Moore's hand, prayed and urged the boy to hold on.

"He was fighting with all he had. Fighting, fighting, fighting," Hardy said. "He just couldn't make it. He just didn't have enough in him."

Moore was pronounced dead at his home.

The shooting was Portland's fourth in a week. At a news conference Tuesday, Mayor Sam Adams said Moore losing his life on the same night as his mother was a "double horrible, horrible tragedy." And he said the rash of violence is a "call to action" for all Portlanders to be vigilant this summer.

Adams urged residents to volunteer for neighborhood watch programs and report any tips to police.

"If you see a gun, call 911," he said. "We have too many guns in the wrong hands."

Though combating gang activity was the focus of the news conference, Police Chief Mike Reese said detectives were still trying to determine whether Monday's shooting had a gang connection. Reese said Moore appears to have been an "innocent victim in the wrong spot," but the suspect may have flashed gang hand signs.

Moore's family and neighbors were adamant he was not in a gang.

The teenager, who moved with his mother from Stockton, Calif., about four years ago, recently graduated from high school, where he was the prom king. He worked at a Salvation Army store, attended church often and planned to take business classes at a community college.

"When you heard the gunshot, Billy was the last person you'd think of," said Jacklyn Hardy, 27, Gabriel's wife. "Instantly you're thinking gang member, hoodlum. The last person you expect to see shot and bleeding would be Billy."

It's unclear what Moore and the suspect were arguing about; a cousin who was with Moore on the bus declined to be interviewed Tuesday.

When asked the same question, the police chief somberly said: "I don't think it was much of anything."