As the word "guilty" filled the silence of a Phoenix courtroom, defendant Michael Marin closed his eyes, put his head in his hands and appeared to put something in his mouth. He then took a swig from a sports bottle.

Minutes later, the 53-year-old Marin was dead.

Now investigators are trying to confirm their suspicion that Marin popped a poison pill after the jury found him guilty of arson, a bizarre ending to a case that began in 2009 when he emerged from his burning mansion in scuba gear.

Prosecutors said he torched his home when he couldn't keep up with the payments. Marin, an attorney and father of four, faced seven to 21 years in prison.

"This is one of the strangest cases I've seen in a long time," said Jeff Sprong, a spokesman with the Maricopa County sheriff's office. "We're hoping to find out exactly what he was thinking and exactly what he took."

Detectives will get the liquid from the sports drink tested for poisons. An autopsy was being conducted Friday to determine if any poison was in Marin's system, but results weren't expected to be released for months.

Marin's four grown children, who live in Arizona, did not return requests for comment, nor did his attorney, Andrew Clemency, or prosecutor Chris Rapp.

Marin, a former Wall Street trader, had summited Everest and wrote on his Facebook page that he had scaled six of the world's seven tallest mountains. He also was an art collector who had original Picassos.