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.