THE DAYS grow shorter and colder, while the body count seems as though it will only grow longer.

The cops hunting the Kensington Strangler know this. As they run down tip calls, pore over neighborhood surveillance footage and scour the desolate, depressed pockets of Kensington for something, anything, that could lead them to the killer, they wonder:

What is fueling the maniac who has murdered two women, maybe three, and possibly led him to choke and sexually assault at least three others? Every idea is in play. But chief among the theories police are investigating is that the strangler was infected with HIV from a prostitute and is now hell-bent on exacting lethal revenge.

"It's a good theory that we are aware of," Deputy Commissioner William Blackburn said last night. "We're trying to figure out why this individual is attacking females engaged in high-risk behavior. That's an idea that we cannot dismiss."

Serial killers are often motivated by ideas and urges that are sexual in nature, he said.

So as detectives continue to try to plunge the depths of the strangler's mind, they have to consider other possibilities, as well, including that he has taken items from his victims as souvenirs.

"There's nothing to indicate that any of them were wearing jewelry that was kept by the perpetrator," Blackburn said, "but it's an idea that we're not dismissing, either."

One thing is for sure: If DNA evidence collected from Casey Mahoney, 27, the East Stroudsburg woman who was found strangled and raped in a lot at Front and Tusculum streets on Wednesday, connects her killer to the slayings of Elaine Goldberg and Nicole Piacentini, investigators will be dealing with a monster the likes of which they haven't seen in a long, long time.

All three women were found partially nude in vacant lots, and Piacentini and Mahoney were found positioned face-down.

"I have almost 30 years on and I haven't seen something like this before," Blackburn said, noting that the strangler - if it is indeed one person - has struck numerous times in a highly concentrated area in Kensington over a short period of time, even as an all-out manhunt has been waged.

"I don't know how many people can say they've experienced a situation like this," he said.

Earlier in the day, police officials released new surveillance footage of a man who beat and choked a 33-year-old woman in an alley on Sergeant Street near Kensington Avenue early Dec. 6.

The alley was the site of a similar attack Oct. 31.

Capt. John Darby, of the police Special Victims Unit, said the man in the footage - a medium-built black man who had long sideburns and wore a hoody while carrying a white iPod - is a "person of interest" in the three murders and two other sexual assaults of women who were choked into unconsciousness. One of the surviving victims helped police create a composite sketch, which the man in the video closely resembles.

Darby said detectives found the new footage, which shows the man sauntering past the alley about an hour before the attack, by poring over "hundreds" of hours of area surveillance footage. Darby said the man appeared to walk with a gait favoring his left leg.

He implored city residents to watch the footage, which is available at the Police Department's website, www.phillypolice.com, and contact investigators at 215-686-TIPS if they recognize the man.

"This is not a phantom. This male did not crawl into a hole," he said. "He's out there. He's interacting with others."

That thought continues to send chills down the spines of people in Kensington, where the strangler is a constant source of discussion and fear.

Yesterday, numerous residents claimed that they heard the strangler was out for revenge because he had been infected with HIV.

"He got burnt. Do you know what that means? It means he was with a hooker and she gave him a disease," said Joey Mershan, 30, who lives in Kensington.

"And now, he has ot nothing to live for cause he's probably going to die. So he's going out on top.

"He's going after as many white hookers as he can. Put yourself in his shoes, do you blame him?" Mershan asked.