Police issued an arrest warrant yesterday for John Lewis after a person close to his family told investigators on Saturday that he or she believed Lewis was the man who fatally shot Cassidy on Wednesday during an armed robbery in West Oak Lane. Cassidy, 54, died the next day.

After receiving the tip, investigators immediately went to the houses of Lewis' mother and grandmother on Roosevelt Boulevard. Sometime before dawn, police developed sufficient evidence to issue the warrant. Authorities believe Lewis had visited his mother's house on the 200 block of East Roosevelt Boulevard on Saturday afternoon, only hours before police arrived.

There is a $153,000 reward for the conviction of Cassidy's killer.

Police said Lewis' mother, Lynn Dyches, is a corrections officer in the Philadelphia prison system. They suspect Lewis used her 9mm semiautomatic to hold up the Dunkin' Donuts on North Broad Street and shoot Cassidy.

The officer was killed as he entered the shop while the robbery was taking place. Police said the assailant wheeled and shot Cassidy in the head from five feet away.

Police have not recovered the murder weapon. The suspect also is believed to have at least one other gun: Cassidy's 9mm Glock service pistol, taken from the officer's side after he fell.

"He is armed and extremely dangerous," Police Commissioner Sylvester M. Johnson said of Lewis at a news conference yesterday morning. "John, if you're listening to us, please turn yourself in."

Lewis is described as 6 feet, 2 inches tall and 270 pounds, a black man with a medium complexion, short cropped hair, and scruffy facial hair. From a surveillance video of the killing, the culprit appears to have a distinctive gait.

Police said Lewis has two tattoos: the initials "HP," for Hunting Park, on his right hand; and "NP," for North Philly, on his left hand. The suspect does not have a spider-web tattoo, as authorities initially announced.

Police said the suspect's family was cooperating with investigators. Lewis' grandmother pleaded through the media for Lewis to surrender.

"John, this is Big Momma. I love you. We want you safe," Vernetha Glover Henry, the suspect's grandmother, said outside her West Roosevelt Boulevard home in Hunting Park.

The suspect, who is known to frequent North Philadelphia and the lower Northeast, also goes by the name Jordan Lewis and sometimes uses Jordan as his last name.

Police advised the public not to approach the suspect, but to call their hotline: 215-683-8888.

Police said they were concerned because they believed the suspect was not afraid to pull the trigger and so an arrest attempt might endanger other officers or the public.

"This male has no hesitation in shooting a person," Johnson said. "If he can shoot a person in uniform as he's coming into a restaurant, coming into a Dunkin' Donuts place, he's liable to shoot anybody."

Added Johnson: "We're begging him. We're pleading for him to turn himself in before anyone else is hurt in the city of Philadelphia."

Lewis, who attended Olney High School only a few blocks from his mother's house, has been arrested before, but not for violent crimes.

In 2005, he was charged with possession of drugs and possession with intent to distribute. He was placed in a treatment program, which he completed in February.

Four months later, Lewis was arrested again on drug charges. That case is pending.