On April 4, police patrolling the neighborhood around the Johnson Homes complex in North Philadelphia stopped to question Quasheam Richburg about a crime. Richburg, 20, with an arrest record involving robbery, gun possession, and assault, ran from the officers and threw a 9mm handgun on the roof of a house before he was caught and arrested, police said.

He was charged with possessing the gun, but posted 10 percent of $5,000 bail. He didn't show up for his May 10 court arraignment, and a bench warrant was issued for his arrest, court records show.

Now, two weeks later, police have issued another arrest warrant for Richburg - this one for Thursday's slaying of Mustafa Shaker, 50, an overnight clerk at Trax Food Store on the edge of Northern Liberties.

At a news conference Friday, police said Richburg shot Shaker in the face with a sawed-off shotgun after Shaker refused to open the cash register during an early-morning robbery attempt. A store surveillance camera captured the killing.

Shaker, an Egyptian immigrant who worked two jobs and had two teenage children, was backing up with his hands in the air when he was shot, said Homicide Capt. James Clark. He died instantly.

Richburg and an unidentified accomplice then tried to pry the register from the counter, police said. They left with nothing.

"This was a cold-blooded and vicious murder," Clark said.

Richburg has had a busy year in the court system.

Besides his April gun arrest, Richburg, of the 2500 block of Ridge Avenue in North Philadelphia, has been charged with two robberies in the last year, according to court records.

In July, at a bus stop near his home, Richburg allegedly smacked, punched, and spit in the face of a 20-year-old woman who was six months pregnant with his child. He then emptied the woman's purse, stealing her cellphone, $21, and a SEPTA TransPass, police reports say.

The woman failed to show up in court, and the case was dismissed Nov. 29.

On Nov. 12, at 27th and Ridge, Richburg allegedly robbed a 30-year-old man at gunpoint in broad daylight, taking the man's cellphone and $18 before running into the Johnson Homes complex, police reports say.

Police arrested Richburg later that day. They said he had a bag of marijuana and a live AK-47 round on him. The gun believed to have been used in the robbery was not recovered. He posted 10 percent of $50,000 bail and was released.

This victim did not show up to testify either. With no witnesses, and with no felony crimes on Richburg's record, prosecutors withdrew the case, said Tasha Jamerson, spokeswoman for the District Attorney's Office.

Relatives recalled Shaker as a friendly man who had been working the midnight shift for three months. He drove a Philadelphia cab by day. Weekends, he visited his two teenage children, who lived in the Poconos with their mother.

He was excited about a website he was developing, called Hearts of Religion, that would promote unity between different faiths, his nephew said.

Police are asking anyone with information about Richburg's whereabouts to call the Homicide Unit at 215-686-3334.

Contact staff writer Mike Newall at 215-854-2759 or mnewall@phillynews.com.