The day before Christmas, the last dispatch to come in to County Cab 36 took driver Gregory Cunningham into Upper Darby.

It was there, in a walkway between two apartment buildings, that the 42-year-old Cunningham's fare took the driver's life with a single bullet to the head, according to police.

The murderer then slid into Cunningham's seat, picked up his cab radio and announced he killed the driver, police said.

Yesterday, Upper Darby Police Superintendent Michael Chitwood named a "person of interest" in the early-morning slaying, calling whoever pulled the trigger "a cold-blooded killer with some psychological problems."

As a result of an intense manhunt and " 'round-the clock" investigation, police said, they were led to the Upper Darby home of Ramir Steve, 19, on Rogers Avenue near Larchwood, the same block where the fare call was requested.

Police obtained a search warrant for the residence. Steve's relatives, including his father, with whom he lives, have been cooperative, Chitwood said.

Since the murder, some family members have heard from Steve, but his whereabouts were unknown, Chitwood said.

Confiscated from the house was a safe that held a .45-caliber semiautomatic handgun, ammunition and identifying information for Steve.

The handgun was reported stolen on Dec. 16, Chitwood said, after Steve visited a friend's house and the friend's father noticed the firearm was missing.

Chitwood said the recovered weapon was not believed to be the murder weapon, though he declined to say what type of gun had been used in the crime.

Cunningham, of Clifton Heights, responded to the fare call around 2 a.m. and about an hour later a man believed by police to be the killer was speaking over his cab radio. Police said yesterday that the killer had planned his crime, though they don't think Cunningham knew his attacker.

Chitwood said Cunningham was most likely forced out of his cab at gunpoint, robbed and "assassinated" where police found his body around 6 a.m. at the Park Lane East Apartments complex on Beverly Boulevard near Sherbrook.

The ransacked cab was found by police about 3:20 a.m. at Keystone and Sellers avenues, about four or five blocks from the murder scene, Chitwood said.

The warrant for Steve's arrest is on the stolen-gun charges, which include receiving stolen property and possessing instruments of a crime. While police are calling him only a "person of interest" in Cunningham's murder, they want him in custody.

"As I speak to you, at this moment, he's out there on the street," Chitwood said. "We consider him a person of interest in the shooting . . . and we consider him armed and dangerous."

Police believe that Steve, who has used other addresses, including Parkside Avenue near Leidy in Philadelphia and Huntley Road near Shelbourne in Upper Darby, is still in the greater Philadelphia area. *