Michael Marin, an outdoor enthusiast and former Wall Street trader, killed himself by swallowing cyanide in an Arizona courtroom moments after he was convicted of arson, officials ruled.

Marin, 53, was sitting at the defendant's table in Maricopa County Superior Court in Phoenix when the verdict was returned June 28.

He was caught on video, slumping forward, head in hands, and he appeared to swallow something that had been hidden in his fingers.

He also drank from a water bottle. He quickly began convulsing and was pronounced dead in the courtroom.

The autopsy report on Marin lists the cause of death as "suicide by cyanide," a spokeswoman for the Maricopa County Medical Examiner's Office said Friday.

The ruling was based on toxicology tests.

Marin was not in custody during his trial. Defendants who aren't in custody and other people entering courthouses aren't strip-searched, so it's possible to hide something like pills in a pocket or elsewhere, said Sheriff Joe Arpaio, whose officers provide security in courtrooms.

The official ruling confirms what had long been suspected.

Police have said they found a canister of cyanide and a note to his son in Marin's car.

Marin said he had earned a fortune trading on Wall Street after earning a law degree from Yale University and building a reputation as a mountain climber.

But times turned hard, according to prosecutors at his trial. Within a year, his bank account went from $900,000 to $50.

He was no longer able to pay the $17,250 monthly mortgage on his Phoenix-area mansion, so he torched the building in July 2009. At the time, he also was facing a balloon payment of $2.3 million on the mansion, owed $2,500 a month on a different home and owed $34,000 in taxes, prosecutors said.

Wearing scuba gear, he fled the 10,000-square-foot mansion fire through a second-floor window and down a rope ladder.

He faced seven to 21 years in prison on the arson conviction.

Arpaio said investigators determined Marin bought the cyanide about a year ago, around the time he reportedly told relatives "he could not go back to jail ... "

Material from The Associated Press is included in this report.