NEW YORK — New York police stepped up the hunt Tuesday for a suspected serial killer after a human skull and bones, potential ninth and 10th victims, were found in separate locations on Long Island.

Police began investigating the so-called "Craigslist Ripper" in December after the remains of four prostitutes, aged 22 to 27, were discovered near Gilgo Beach, a sandy getaway just one hours drive east of New York.

The victims, who worked through online ads posted on the Internet site Craigslist, disappeared on different dates between 2007 and 2010.

Investigators found four more decomposing bodies early last week.

The remains of the possible ninth and 10th victims, like the others, were discovered on Monday on the northern side of Ocean Parkway, the main road that traverses Jones Beach Island -- connected to Long Island by a causeway.

"We found remains at two different locations. In one location we found bones, and two miles (3.2 kilometers) away we found a skull. They appear to be human remains," police spokesman Kevin Smith told AFP.

"They will be taken to the medical examiner for examination," Smith told reporters.

Police did not rule out that the skull and the other bones could belong to the same person even though they were discovered miles apart.

Like the four bodies discovered last week, they are yet to be identified and there is no evidence yet apart from their geographical location to link them to the suspected serial killer.

The first bodies were discovered while police were searching for Shannan Gilbert, a 24-year-old prostitute from New Jersey reported missing after meeting a client in nearby Oak Beach in May 2010.

She was not among the first four bodies identified and remains to be found.

If a serial killer is on the loose in the area, it would be the third such case in the region over the past 20 years.

The most notorious was Joel Rifkin, who is serving a life sentence for the murder of nine women, most of them drug addicted prostitutes, between 1989 and 1993. He is suspected of having killed as many as 17.