A wealthy stock trader's negligence led to a deadly fire that killed a young man who was helping him build a network of tunnels for a bunker beneath a suburban Washington, D.C., home, a lawsuit alleges.

The parents of 21-year-old Askia Khafra sued 27-year-old Daniel Beckwitt and his father on Monday, the anniversary of the fire that killed Khafra in the basement of the Beckwitts' house in Bethesda, Maryland.

Daniel Beckwitt is charged with second-degree murder and involuntary manslaughter in Khafra's death. His criminal trial is scheduled to start in April 2019.

The "hoarding conditions" in Beckwitt's home made the fire spread more quickly and created a maze of junk and trash that hindered Khafra's ability to escape, the parents' wrongful death lawsuit says.

Beckwitt didn't immediately respond to a phone call and text message seeking comment on the lawsuit, which the parents filed in a Montgomery County court. An attorney who represents Beckwitt in the criminal case has called Khafra's death a tragic accident, not a crime.

Investigators found Khafra's charred body in the basement, where a hole in the concrete floor led to a shaft that dropped down 20 feet (6 meters) into tunnels that branched out roughly 200 feet (60 meters) in length.

During a hearing in May, Montgomery County prosecutor Douglas Wink described Beckwitt as a skilled computer hacker who had a paranoid fixation on a possible nuclear attack by North Korea.

Beckwitt's lawyer, Robert Bonsib, described his client as a successful "day trader" who has made millions trading stocks.

Khafra, who lived with his parents in Silver Spring, had met Beckwitt online and agreed to help him dig the tunnels in exchange for Beckwitt's investments in an internet company Khafra was launching.

Dia Khafra, Askia Khafra's father, said during a recent interview that he and his wife, Claudia, tried to persuade Askia to stay away from Beckwitt's tunnels.

"I always feared something dangerous would happen to him," the elder Khafra said.

Beckwitt went to elaborate lengths to preserve the secrecy of his tunnels, tricking Askia Khafra into thinking he was digging them in Virginia, not Maryland, according to authorities.

Beckwitt told investigators he would rent a car, pick Khafra up and drive him to Manassas, Virginia, where he had the younger man don "blackout glasses" before driving him around for about an hour, a police report said. Khafra spent days at a time working, eating and sleeping in the tunnels. He had his cellphone with him, but Beckwitt used internet "spoofing" to make it appear he was in Virginia, according to Wink.

The tunnels had lights, an air circulation system and a heater powered by a "haphazard daisy chain" of power strips that created a fire risk, Wink said.

"These extension cords and power strips created a clear and substantial risk of fire, exacerbated by the piles of paper and garbage throughout the house, and the storage of dangerous chemicals," the parents' lawsuit says.

Wink said Beckwitt ignored "obvious signs" of danger before the fire broke out Sept. 10, 2017. Hours before the fire, Khafra texted Beckwitt to warn him it smelled like smoke in the tunnels. Beckwitt flipped a breaker that turned off lights in the tunnels but turned the power back on after Khafra said he couldn't see, Wink said.

County officials sued Beckwitt over the property's condition, calling it unsafe and a "public nuisance." Beckwitt's father, David, owns the Bethesda property but lives in Burke, Virginia, according to the wrongful death lawsuit.