FRANCIS ZARZYCKI had been inside that rundown Center City apartment - the one with the prostitutes - but this time, something went wrong.

It was Aug. 26, and Zarzycki had just met up with two young women inside Apartment 26 at 220 S. 11th St., when their alleged pimp, Keith Tolbert, emerged from another room.

This wasn't business as usual. Tolbert and the alleged hookers, Angel Weston and Stephenie Foulke, wanted to rob Zarzycki, police said.

The Northeast Philly resident wasn't having it, and the ensuing struggle set into motion a truly gruesome chain of events that only came to light Tuesday morning, when a boater found Zarzycki's torso floating inside a bag in the Schuylkill.

Homicide Capt. James Clark said yesterday that Zarzycki, 40, was zapped with a stun gun during his struggle with his would-be robbers, then suffocated. In the sickening moments that followed, Tolbert allegedly used a hatchet to hack up Zarzycki's body in a bathtub.

It's unclear how or when the killers dumped his remains into the river.

Investigators were able to identify Zarzycki by a distinctive tattoo on his back. Zarzycki's head, arms and legs have not yet been found, Clark said.

Tolbert, 34, Weston, 21, and Foulke, 22, have all been arrested and charged with murder.

Clark said detectives are continuing to interview the three accused fiends with the hope that Zarzycki's remains - and the murder weapon - can be found.

Crime Scene Unit officers last night removed a portion of a pipe that was connected to the tub, while other investigators eyeballed hours of surveillance footage from nearby cameras to see if more evidence of the crime could be found. Marine Unit cops were also expected to again scour the murky waters of the Schuylkill.

Zarzycki's family reported him missing to Northeast Detectives last week. Cellphone records and information on his computer led investigators to the apartment building on 11th Street near Locust.

"I know it wasn't his first time there," Clark said.

Citywide vice cops ran a sting operation at the apartment Saturday, and busted Tolbert, Weston and Foulke on prostitution-related offenses.

"I don't know why they decided to rob him," Clark said. "I don't know how much money they thought he'd have."

According to news reports, Zarzycki worked as a loan officer for a PNC Bank in Doylestown, but also struggled with a drug problem in the past.

No one answered the door yesterday at Zarzycki's home on Endicott Street near Poquessing Creek Drive. A neighbor yelled at reporters to leave the family alone. According to a law-enforcement source, Zarzycki's father, Frank Zarzycki, is a retired Philly cop who left the force in 1989.

Yesterday afternoon, as investigators hauled bags of evidence out of the Center City apartment building where Zarzycki's slaying took place, residents of the building - which is Section 8 housing - complained about a lack of security there.

"It's not safe here," said Kafi Roundtree, 41, who uses a wheelchair and has lived in the building for 21 years. "I feel as though the manager should be considerate of the residents here. They haven't notified us [about the slaying]. They are keeping it very hush-hush."

Roundtree said she lives next door to Tolbert's apartment, where the alleged slaying and subsequent dismemberment was carried out, but that she didn't hear anything that raised her suspicions.

Tolbert and friends of his would sometimes have music on late into the night in the apartment and party, she said, but nothing ever seemed amiss.

"Keith seemed like a regular neighbor," she said, adding that the man had moved in only a few months ago.

"I'm not even [living] a foot away from the man . . . I live by myself with home health-care aides," Roundtree said. "I'm very shaken by it and I want to move right now. We've been fighting for security for years now."

A woman who answered the phone in the manager's office for the building, called Washington Square West, hung up on a Daily News reporter yesterday.

Another resident of the building, who declined to give his name, said drug dealing has been a major problem in the 10 years he's lived there. He wasn't aware of prostitution in the building, though.

"It's not safe," he said. "Someone else is going to get killed in there. That's the feeling I have."

A police source familiar with the neighborhood said the address hasn't been a location known to cops for prostitution, but that last week, vice officers made two other prostitution-related arrests there.