WASHINGTON (THE WASHINGTON POST) - A millionaire day-trader who was having a secret bomb shelter and tunnels built under his home in Bethesda, Maryland, was found guilty of murder on Wednesday (April 24) for creating work conditions that prosecutors called a "death trap".

Daniel Beckwitt, 27, faces up to 30 years in prison after a jury in Montgomery County concluded he had committed "depraved heart" second-degree murder in the death of Mr Askia Khafra, 21, whom Beckwitt had hired for excavation work.

In reaching the verdict, jurors determined Beckwitt had acted in "extreme disregard for human life".

The tunnel system dropped 6m from Beckwitt's basement, and expended up to 61m in at least three directions.

Mr Khafra had been working in the tunnels on the afternoon of Sept 10, 2017, when an accidental electrical fire broke out in the home's basement.

Mr Khafra smelled smoke, climbed out of the tunnels and tried to escape through the basement. But he was slowed before he could reach a doorway by hoarding-like clutter and perished from smoke inhalation and thermal injuries, according to prosecutors.

"He was stuck in a death trap," Assistant State's Attorney Marybeth Ayres had told jurors during the two-week trial. "He could not get out."

"This case is about an accident, an accident pure and simple," countered Beckwitt's attorney, Mr Robert Bonsib.

"An accident that involved the death of a fine a young man. An accident that occurred under circumstances that were completely unintended and unexpected by another fine young man."

The jury deliberated for two hours on Tuesday and all day on Wednesday.

Beckwitt had gone to extreme measures to keep his bunker a secret, starting the project several years ago without his neighbours being aware of it.

He did not hire professional excavators, but over time enlisted at least three acquaintances to dig. One of them, Mr Khafra, started working in early 2017. Beckwitt had met him online, and invested US$5,000 (S$6,810) in a start-up financial venture Mr Khafra was trying to launch.

Beckwitt tried to keep the location of his home secret from Mr Khafra. He would pick Mr Khafra up at his home in Silver Spring and ask him to wear blacked out glasses, according to trial testimony.

Beckwitt maintained to Mr Khafra that his bunker was in rural Virginia, according to trial testimony. To keep up the ruse, Beckwitt would drive the younger man around for an hour before pulling up to his home along Danbury Road, several blocks north of the National Institutes of Health.

In recent interviews, Beckwitt's neighbours said they knew nothing about the tunnels before they came to light after the fire.