Raheem Grant's look of innocence, his smallish physique and his smile, seen on a makeshift memorial set up yesterday in Overbrook, belied the deadly trouble that lurked there.

According to police, Raheem, 15, who lived in the neighborhood, was shot once in the back of his head at 63rd and Callowhill streets about 2:20 a.m. Saturday.

He was pronounced dead at the scene, and investigating detectives said only that they believed his killing was "retaliatory."

Meanwhile yesterday, homicide detectives were piecing together the details that led to the shooting death of an unidentified 29-year-old man inside his East Germantown home.

Police were called to a home on Morton Street near Washington Lane shortly before 3 a.m. and found the man with multiple chest wounds. He was pronounced dead shortly after police arrived.

Homicide detectives said they also identified a man arrested and charged with the murder of his girlfriend, Yumi Demicco, 24, who was found dead in their Wynnefield Heights apartment Saturday afternoon.

William Johnson, 36, was charged with murder, possession of an instrument of crime, and related offenses, police said.

Homicide Lt. Philip Riehl said Demicco was killed July 21 after an argument with Johnson. Police said she died from blunt-force trauma to her head.

After Johnson allegedly killed Demicco, he drank windshield-washer fluid in an apparent suicide attempt, cops said yesterday.

Also arrested yesterday was Steven Connolly, 34, of Levittown, Bucks County.

Connolly is charged with the murder of William Glover, 49, a disabled and unemployed train worker.

Police said Glover was stabbed multiple times in the neck on 10th Street near Schiller in North Philadelphia about 1:40 p.m. Saturday.

Glover died Saturday night at Temple University Hospital. Riehl said Glover was killed over a "drug debt."

In Overbrook yesterday, the news that Raheem Grant may have been killed as retaliation caused little shock in a busy neighborhood where many people work during the day.

"It's really crazy," said a woman, who called herself a lifelong resident of the neighborhood.

"There was an explosion a week ago, and there's shootings all the time," she said.

The woman, who did not want to be identified, paused near the multicolored makeshift memorial at 63rd and Callowhill bearing Raheem's picture, candles and teddy bears.

Other neighbors agreed that the neighborhood had gone from bad to worse.

They blamed groups of youths for much of the trouble.

"What was he doing out so late?" pondered Jason Miller, a resident of nearby Felton Street.

"I don't know the situation, but why would a 15-year-old be out past midnight?"

Hanging out late at night shouldn't be a thing for young folks, agreed neighbor Roberta Jenkins.

"The neighborhood is pretty bad . . . ," she said.

"Someone I know just got shot two weeks ago. I'm trying to move."

Darnell Washington, who also lives in the area, said it was hard to believe that Raheem could have been shot over a misunderstanding or an argument.

"He was real cool . . . ," said Washington. "Shot in the head? That's crazy. Who deserves that?"

Many passers-by stopped to check out the memorial to Raheem. But in a city gripped by a "don't snitch" mantra, not many would say anything about the shooting.

One woman said she knew Raheem, but hurriedly walked away when approached by a reporter.

"I'm sorry," she said, as she walked down 63rd Street.

"I'm sorry, I'm not going to say anything."