A pair of Highway Patrol cops chased a convicted murderer in a pickup truck through Frankford on Tuesday, believing he had just kidnapped an infant.

Boy, were they in for a surprise.

When the cops finally caught up with Shawn Jason on Ditman Street near Wakeling, police said, they realized that he didn't have a baby - just a truck that wasn't his, a piece of luggage, $8,980 in cash, some crack and marijuana and a loaded 9 mm handgun.

"Pretty unusual case," said Highway Patrol Capt. Michael Cochrane.

Cochrane said Officer Joe Hanson and Sgt. Mike Walton were riding in their patrol car about 11:25 p.m. when they saw Jason, 33, arguing with a woman at Tackawanna and Wilmot streets.

"They saw him reach into a car and grab what appeared to be a child seat with an infant in it, then jump into a green Dodge pickup," he said.

Jason sped off, and the Highway Patrol cops gave chase. During the pursuit, Cochrane said, Jason appeared to fiddle with the truck's driver-side control panel.

Jason, who has 12 prior arrests, abruptly stopped after driving five blocks and was immediately handcuffed by the officers, Cochrane said.

Hanson eyed the truck's control panel and noticed it was slightly askew. Moments later, he removed the panel and found a loaded Taurus 9 mm handgun stuffed inside, Cochrane said.

After checking the handgun's serial numbers, investigators determined that Jason did not own the weapon or have a permit to carry it.

A further look inside the truck turned up a clear plastic baggie with 25 grams of crack and two rectangular vials that contained 32 grams of marijuana, Cochrane said.

Jason was charged with weapons and drug offenses.

In 1998, he was convicted of second-degree murder in the shooting of 17-year-old Ryheem Furchell during an attempted robbery.

Jason's cohort in the crime was Dirrone Tindal, 18, who was convicted of first-degree murder for firing the fatal shots.