Officials say a state police officer with a dog located the first set of bones on the north side, about one and a half miles from the tower at Jones Beach.
A skull was found in another location a few hours later, officials said. Authorities were trying to determine if the skull is linked to the initial set of remains or another body altogether.
About 125 searchers, some with dogs and others on horseback, scoured the area Monday.
"We want to bring to justice this animal that has obviously taken the lives of a number of people," Nassau County Executive Edward Mangano said during an early afternoon briefing.
The other bodies were found about five miles away in neighboring Suffolk County to the east.
Meanwhile, sources tell Eyewitness News one of the four bodies found last week was that of a baby not even two years old.
The four remains found in the latest sweep are still unidentified, though police have ruled out any of the victims to be the still missing Shannon Gilbert.
Gilbert, a Jersey City prostitute was the initial focus of the investigation.
The search in Suffolk County started back in December, and with snow storms and frozen ground, it stretched on for three months. Police found the remains of eight bodies, four of which have been identified. The earliest disappearance stretches back almost four years, to July of 2007.
Gilbert's mother told Eyewitness News after her daughter vanished, she received a strange call from a man from Oak Beach, who said Gilbert had been in his house the night she disappeared.
That man is among as many as several persons of interest ABC News has learned investigators are considering.
But there are no quick answers. And security expert Michael Balboni says the more bodies turn up, the greater the chances of catching this killer.
"There's some obvious factor here. It's more and more looking like it's local because how do you take nine bodies down to the beach? It's not something you can do from Philadelphia, from upstate New York," Balboni said.
There is increasing suspicion the killer could be someone familiar with law enforcement methods. One reason is that six calls were made to the sister of one victim using the dead woman's phone, and all the calls were too short to trace. They were also made from hyper-busy locations like Penn Station, where the caller would not stand out on surveillance cameras.
That reasoning could explain the meticulous placement of the bodies: two different sets, placed in different ways. The first four skeletons were reportedly wrapped in burlap and closer to the road, while the next four were dumped much deeper in the thick brush.
"It could be some that works as a civil servant, that could be a code enforcement person, could be a building inspector, could be a postman," former NYPD detective Wally Zeins said. "Or it could anyone who knows the area quite well."