In September, 21-year-old Askia Khafra was found dead after a house fire in a suburban Bethesda home belonging to security researcher Daniel Beckwitt. Now, Beckwitt has been charged with murder in connection with Khafra’s death. Prosecutors say Khafra had been hired to construct an intricate network of tunnels below Beckwitt’s home, and that his death resulted from unsafe working conditions.

According to court documents, the tunnels were dug 20 feet below the basement of the home, spanning as far as 200 feet. The tunnels were constructed under extreme secrecy, with local permitting agencies unaware of the full extent of the construction. Khafra arrived at the work site wearing black-out glasses to prevent him from knowing its location; throughout the construction, he believed the house was in Virginia.

It’s still unclear how Beckwitt planned to use the underground structure, although his lawyer told a local news station that he planned to “create a secure bunker because of his concern for international threats, including from North Korea.” After the fire, the city cited the project for a number of code violations, believing that the tunnels likely extend beyond the house’s property line.

Beckwitt had found significant success as a hacker, presenting research at security conferences like DefCon and SchmooCon. In 2013, he was arrested in connection with a series of pranks at the University of Illinois — known as the ECE Hacker campaign — but prosecutors ultimately declined to press charges.

Prosecutors claim the fire was the result of an unconventional construction setup, which included a so-called “daisy chain” of extension cords to provide power for the equipment. Significant amounts of trash had also accumulated in the home, making escape more difficult. Taken together, prosecutors argue the conditions amounted to a reckless disregard for human life. Beckwitt was inside the home when the fire broke out, but escaped to tell responders that Khafra was still inside.