New York State Police search brush near Field 6 at...

New York State Police search brush near Field 6 at Jones Beach as the investigation in to an apparent serial killer expands. (April 11, 2011) Credit: James Carbone

Nassau and State Police will return again to a South Shore barrier island Friday to search near the spots where human bones were recovered this month, officials said Thursday.

The canvass by Nassau County police will be focused in a wildlife sanctuary at Tobay Beach, where investigators found a human skull and attached vertebrae on April 4.

Hours earlier, New York State Police working to the west of the sanctuary found a plastic bag holding human bones in a recently dug excavation site along Ocean Parkway. "We're having a limited search where one of the remains was found," Nassau police Det. Lt. Kevin Smith said Thursday.

State police will also conduct a follow-up search, to begin at 9 a.m., said State Police investigator William Hulse. The parkway is expected to remain open to traffic.

Sources with knowledge of the skull discovery have said it appears to be of a woman, but is likely too old to be Shannan Gilbert, 24, whose disappearance has prompted several searches of the area. The bones are believed to be from human legs, the sources said.

One search for Gilbert, of Jersey City, who was last seen alive on May 1 in Oak Beach, led to the December discovery of four skeletons dumped in the Gilgo Beach area. All are young women who worked as prostitutes and are believed to be a serial killer's victims.

In March and earlier this month, Suffolk police recovered four more sets of remains during a search for Gilbert, including those of a young child wrapped in a blanket and an adult that showed signs of dismemberment, according to sources with knowledge of the investigation. Gilbert has been excluded from those finds.

Police officials are awaiting results of an FBI aerial operation completed Monday to create a high-resolution image of the island to be examined for signs of more bones.