Whoever killed four prostitutes, and possibly four other people, and then dumped their bodies in heavy underbrush along a beachfront causeway on Long Island appears to have a sophisticated understanding of police investigative techniques, according to people briefed on the case.

A series of taunting phone calls made to the teenage sister of one of the victims — calls that the police suspect came from the killer — were made from in or around some of the most crowded locations in New York City, including Madison Square Garden and Times Square, according to the people briefed on the case and to the mother of Melissa Barthelemy, that victim.

The locations, detectives say, were probably chosen because they allowed the caller to blend into crowds, so that if investigators pinpointed his location from the cellphone’s signal, they would be unable to pick him out of the crowd using any nearby surveillance cameras, one of the people said.

This fact, as well as the killer’s use of disposable cellphones to contact the four victims who have been identified — women in their 20s who advertised their services on Craigslist — suggested to some investigators that the killer was well versed in criminal investigative techniques, gleaned either through personal experience or in some other way, and could even be in law enforcement himself.