An autopsy on 11-year-old New Hampshire girl Celina Cass, whose body was found in the Connecticut River a week after she went missing, could not immediately pinpoint on Tuesday how she died.

Investigators were awaiting results of toxicology tests and further investigation, said Jane Young, a state prosecutor in the New Hampshire attorney general's office.

"The death certificate indicates both the cause and manner of death are still pending," Young told reporters. "The attorney general's office continues to investigate her death as suspicious."

Cass, who had long brown hair and hazel eyes, went missing on July 25 from her home in West Stewartstown, New Hampshire, near the state's border with Canada. The FBI received more than 500 tips in the case and offered $25,000 for information leading to her whereabouts.

Divers from New Hampshire's Department of Fish and Game located the girl's body on Monday in the river near a hydroelectric plant in the community of about 1,000 people.

The decision to open a criminal investigation in the girl's death was based on visual evidence from the girl's body both in the water and when viewed on shore, Young said. She declined to comment on whether police had identified any people of interest in the case.