A guilty verdict, a mouthful of poison – and minutes later he was dead

US millionaire appears to commit suicide in the dock after being convicted of arson

Police in Arizona are awaiting post-mortem results on a former Wall Street trader, art collector and millionaire who collapsed after being found guilty of arson in what may turn out to be a case of in-the-dock suicide.

Michael Marin, who had been charged with setting his own home on fire in 2009 in the hope of collecting insurance money to cope with mounting debts, buckled in gulping convulsions on the courtroom floor within minutes of the guilty verdict being read on Thursday afternoon. He was later pronounced dead in a local Phoenix hospital.

Investigators are poring over footage from a television camera that was inside the courtroom. It shows Marin grimly absorbing the verdict, which could have spelled a sentence of up to 16 years in prison, and then putting his hands to his face. He looks at that moment to be putting something into his mouth and swallowing, though no pill or substance is actually visible on the tape. He then took a drink from a bottle of water.

Officials confirmed that suicide is suspected. "They are leaning towards that. If you watch the video it looks like he does put something in his mouth," Sheriff's Office spokesman Jeff Sprong told a local Fox television station. "We cannot verify that at this point and we're not going to be able to until the toxicology report comes back."

Once a high-roller who flew planes, climbed eight of the world's tallest summits, including Everest and collected art – in particular Picasso sketches – Marin had said he had survived the blaze in his $3.5 million mansion in the Biltmore section of Phoenix only by grabbing his scuba oxygen bottles, using them to breathe, and escaping down a fire ladder from the second floor. But fire officials said they found evidence that the fire had been started deliberately.

"Michael Marin couldn't pay his mortgage, so he burned down his house," prosecutor Chris Rapp said in opening statements of the trial. He described to the jury how in the year before the inferno, the defendant's bank account had run dry as a balloon payment on his house of $2.3 million was due. An attempt by him to sell the house in a charity raffle had also come nothing after local authorities said it would be illegal.

While no one was hurt in the fire at the Marin home, the penalties for arson in Arizona are particular stiff – roughly equal to sentences typically given out for second degree murder.

The jury had been sent out by Judge Bruce Cohen and the lawyers were at the bench discussing the sentencing phase of the case, when the drama at the defendant's table begun. A reporter for the Arizona Republic writes that Marin went puce in the face and grabbed a tissue from a woman behind him. Very soon after that, he fell face first on to the floor of the courtroom making gasping sounds and vomiting. By then, his cheeks were ashen.

No one in Arizona could remember any precedent of the events, particularly if it turns out that Marin indeed poisoned himself to avoid going to prison. "I'm at a loss for words, honestly, at this point," Judge Cohen said. The Sheriff's office agreed. "This is something new that I've never seen and I'm sure the courts haven't seen it," Mr Sprong said.