An independent autopsy on Shannan Gilbert, whose disappearance in 2010 led to the discovery of the Gilgo Beach slaying victims, suggests she was strangled.

There is no evidence that drugs or drowning led to the death of Gilbert, 24, former New York City medical examiner Dr. Michael Baden said in his report released Friday.

The attorney for the Gilbert family, John Ray of Miller Place, used the report to demand that Suffolk police reopen its investigation into Gilbert’s death and treat it as a murder.

“We have been very unhappy with the behavior of the Suffolk County Police Department,” Ray said at a news conference Friday. “It has been a poor, really awful investigation. We are distressed by that.”

Police Commissioner Timothy Sini said in a statement that police have reviewed Baden’s report. He said the police department “is doing everything it can to solve the Gilgo Beach homicides and that is why the department recently partnered with the FBI.”

Gilbert’s body was found in December 2011 in a damp thicket at Oak Beach.

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Baden’s autopsy, performed last March, did not determine a cause of death and found nothing that the Suffolk medical examiner’s office didn’t find.

The findings differ in their interpretation of the condition of the hyoid, a small, U-shaped bone in the neck. When people are strangled, this bone is often cracked or broken.

The tips of Gilbert’s hyoid bone were missing and the edges were rough. The official autopsy suggested this and other damage to the decomposed body were consistent with an animal gnawing it.

Baden wrote that the rough edges were consistent with fractures caused by “homicidal manual strangulation.”

“It’s time now for the police department to wise up,” said Ray, who asked Baden to do the autopsy. “It’s time to do the job they have failed to do up to this point.”

Mari Gilbert and her surviving daughters believe Shannan was murdered.

“She’s not perfect. No one’s perfect,” said Mari Gilbert, of upstate Ellenville. “But she was loved.”

Gilbert, a sex worker from New Jersey, vanished on May 1, 2010, after being summoned to a client in Oak Beach. Police said she was last seen fleeing the client’s home in a panic.

She reportedly made a 911 call, saying unnamed people were trying to kill her. Ray said he has tried without success to get the police department to give him a recording of that call.

In December 2010, a K-9 officer conducting a routine exercise and searching for Gilbert stumbled on another woman’s body in a thicket of bramble in Gilgo Beach that eventually led to the discovery of a dumping ground of 10 sets of remains along Ocean Parkway.

Ever since, Gilbert’s death and the mystery of who killed the others have confounded investigators. They have said Gilbert’s death is not linked to the other victims found.