An autopsy result on Celina Cass, whose body was discovered on Monday in the Connecticut River after a week-long massive search, returned inconclusive, Tuesday, deepening the mystery behind the cause of her death.

“The cause and manner are still pending,” said Jane Young, a state prosecutor in the New Hampshire attorney general's office.

Investigators are awaiting "toxicology results and further investigation," she said. "The attorney general's office continues to investigate her death as suspicious."

In order to preserve the "integrity of the investigation," Young declined to give any further comments, just saying "we are doing everything we can to have more definitive answers."

Celina, an 11-year-old girl, who lived with her mother, sister and stepfather in West Stewartstown, New Hampshire, was last seen at home before her computer at about 9 p.m. local time on July 25. Next morning when her parents went to wake her up, they found she had disappeared, authorities said.

The police said her disappearance was mysterious as there was no sign of any struggle or any indication of her whereabouts.

Last week, over 100 federal, state and local law enforcement officers conducted a massive search over a mile-wide area around her home, even in the woods and ponds.

The FBI offered a $25,000 reward for any information, which can lead to her whereabouts and received over 500 tips.

However, Cass's dead body was finally found in the Connecticut River near her home on Monday by a dive team from the New Hampshire Fish and Game Department.

Wendell Noyes, Celina's stepfather, went to hospital before her body was found in the river on Monday. On Tuesday he returned home.

According to witnesses, Noyes was taken to hosptial by ambulance. On Tuesday morning, Shannon Towle, owner of Towle's Mini-Mart, sold him cigarettes.

The Celina's death left her family and friends in mourning. Adam Laro, Celina’s father recalled her as “everyday child who loved being in life”. He said, “I can’t see why someone would want to do that to my daughter. … She was very kind in spirit.”