Police are considering the possibility that the serial killer who has dumped at least eight bodies along a Long Island barrier beach may be an ex-cop or other law officer, law enforcement officials familiar with the case said.
The possibility that the killer could be a former law enforcement official or other person with knowledge of law enforcement techniques is being considered based on evidence that the suspect may understand investigators' procedures, they said.
Numerous people with possible links to the four slain women who have been identified have come to the attention of police since the investigation began, the officials said.
Police are also looking at people who have had regular or routine access to the beach where the bodies were found, and investigators are also exploring possible links to the serial killer who murdered prostitutes in New Jersey, they said.
"[The killer] could be law enforcement, could be a civil servant, could be a code enforcement person, could be a building inspector, could be a postman ... or it could be anyone who knows the area quite well," former New York Police Department detective Wally Zeins told ABC News.
One clue that the killer may have a detailed knowledge of police techniques is that he or she allegedly placed several taunting phone calls to a murder victim's relative, according to those familiar with the case.
The calls were placed from crowded spots like New York's Penn Station, where even if police were able to trace the cell signal, it would be next to impossible for surveillance cameras to single out the killer.
"The caller always stayed on the phone for under three minutes -- which indicated that he or she knows that it takes the police from three to five minutes to trace the call," Rod Wheeler, former homicide detective told "Good Morning America."
"Most of these telephone calls that have gone out to the deceased have been a male's voice, so from that you have to assume it's probably a male that's doing these crimes," he added.
According to one investigator familiar with the case and the behavior of serial killers, this appears to be an organized serial killer who plans methodically and is probably above average intelligence. It appears that the killer usually lures people, kills them in one place and then disposes of the body in another.
This sort of killer is often social -- not a loner -- with family, friends and what would appear to be a normal life, the investigator said.
It was the disappearance of a prostitute that led New York police to stumble on the serial killer's ocean-front dumping ground in western Suffolk County.
Shannan Gilbert, 24, disappeared in May 2010 after arranging online to meet a client. Her disappearance triggered a search in the scrub brush along Gilgo Beach, a popular summer getaway spot, but much less frequently visited in the winter.
In December police found four skeletal bodies, all of them women and all of them prostitutes, but none were Gilbert.
Police say Gilbert met a man named Joseph Brewer on Craigslist the night that she disappeared, but so far he has been cooperative with their investigation and isn't a suspect. There are now new reports a second man was seen partying with Gilbert the night she went missing, but so far no arrests have been made.
Last week, cops found another four bodies. Those bodies have not been identified, but Suffolk County Police said Tuesday that none of the remains belonged to Gilbert.
Cops obtained DNA samples of Gilbert's family last year and were able to quickly check the remains against those samples.
The police conclusion suggests that Gilbert is possibly a ninth victim of a serial killer.
Cops searched the brush along Gilgo Beach and neighboring Oak Beach last week, looking for the bodies of more women potentially killed and dumped in the thick vegetation, while other detectives worked to create a profile of the man who is stalking prostitutes online and killing them.
Suffolk County police have kept a tight lid on many of the investigation's details, commenting publicly only on the search efforts, including the canine units with cadaver sniffing dogs and a dozen police recruits from the academy brought in to help search for bodies.
In December, while searching for Gilbert, police stumbled on the killer's dumping ground, an area that has turned out to be a seven-mile stretch of beach as more bodies were discovered.
Zeins is confident that the killer will eventually slip up.
"The reason why we put erasers on pencils is because we all make mistakes. Whoever it is will make a mistake, and they'll get caught," he said.
Brad Garrett, an ABC News consultant and former FBI agent who has investigated dozens of high profile cases including the death of Washington intern Chandra Levy and the 2001 anthrax mailings, said he feels there is a distinct connection between the killer and the area.
"Given the volume of bodies in one location, it tells me the killer is very familiar with this stretch of road," Garrett said. "He grew up there, works there, lives there, or has a reason to frequent area. He feels comfortable stopping on that road at least eight times and dragging women to the sea grass line without worrying about being caught."
Though the profile of the Long Island killer is specific to the clues he has left behind, experts say there are typical traits many killers tend to have.
On average serial killers are white men between the ages of 20 and 40. They were often abused as children, but rarely have criminal records. They typically do not travel far to commit crimes, preferring instead areas they are familiar with and which they can move about without raising suspicion.
Serial killers are also often under-employed, Garret said, and clues at the beach may help investigators determine his job, an important step in narrowing the circle of suspects.
"Some of the women were wrapped in burlap bags," Garrett said. "It's possible that that those bags came from some aspect of his life. Did they have fertilizer in them? Did they have coffee? What might that mean about his job?"
Garrett, however, said that does not mean investigators should immediately assume the killer is a "blue collar transient type."
Instead it's feasible that the killer "leads a normal life," he said. He "could be married and functions well in society. But he has this other dark side to his personality."
Serial killers often target prostitutes, said Jack Levin, a criminology professor at Northeast University who studies serial killers.
"The most common victims are prostitutes," he said. "They're easy prey. They get right in the car with a killer. Families are slow to file missing person reports and there is little pressure on police to solve the case because it's a criminal killing a criminal."