ST. PETERSBURG, FLA. -- The initial autopsy on the remains of Brian Laundrie did not uncover a cause of his death and a more intensive examination will be done, a Laundrie family lawyer said Monday.

Laundrie's skeletal remains found in a Florida nature preserve were positively identified last week using dental records, according to the FBI. Laundrie was the subject of a manhunt for more than a month as investigators searched for clues in the slaying of his girlfriend, Gabby Petito, during their cross-country van trip together.

Steve Bertolino, the Laundries' attorney, said in text messages Monday that he was told by police the autopsy by the Sarasota County medical examiner did not produce concrete results on Brian Laundrie's death.

"I was told the manner and cause of death were not determined and the remains were sent to an anthropologist (for) further evaluation," Bertolino said.

The medical examiner's office declined comment Monday, as did the FBI office in Denver that is leading the probe.

Eventually, Laundrie's remains will be cremated and no funeral is planned by his family, Bertolino said.

No information has yet been released on what investigators found in a backpack and notebook found with Laundrie's remains.

Petito, 22, was discovered slain last month on the edge of Grand Teton National Park in Wyoming, one of the places the young couple had visited on the trip they documented through social media videos.

An autopsy in Wyoming concluded Petito died by strangulation and that it was a homicide. Laundrie, 23, was listed as a "person of interest" in her killing but he was charged only with fraudulent use of a debit card that was not his.

His remains were found in a nature preserve not far from his family's home in North Port, Florida, where both he and Petito had been living. Both were originally from Long Island, New York.

Laundrie returned home alone Sept. 1 from his trip with Petito. Her body was found Sept. 19 in the Wyoming park and authorities say it had been there for about a month.

Laundrie told his parents Sept. 13 he was headed to the Carlton Reserve park in Sarasota County. That was the last publicly known contact anyone had with him.