A self-proclaimed neo-Nazi was arrested in Florida Sunday after police found materials used to manufacture explosives in his apartment. The case was directly related to a double murder that occurred in a Tampa apartment building Friday where a former neo-Nazi who converted to Islam killed two people for “disrespecting the Muslim faith.”

Tampa police and the FBI found a material inside Brandon Russell’s garage that tested positive for hexamethane triperoxide diamine, used to make explosives, the Miami Herald reported Monday. Authorities also found empty bullet casings with fuses that could be used to detonate the material. Inside Russell’s bedroom was a framed photograph of Timothy McVeigh, the man who bombed a federal building in Oklahoma City in 1995. Police also located white supremacist and Nazi propaganda and detected the presence of radiation coming from thorium and americium.

Read: Florida Neo-Nazi Who Converted To Islam Kills Two For Disrespecting Muslim Faith

Russell was arrested on possession of unregistered destructive devices and unlawful storage of explosive charges. He told authorities the explosives were from a rocket-making project he was working on in 2013 for the engineering club at the University of South Florida to propel balloons into the atmosphere. FBI agents, however, said the materials they found were “too energetic and volatile” to be used for such purposes.

Russell did not immediately respond to the charges.

The FBI didn’t say why Russell was in the Keys or why he had been pulled over. Russell told the FBI upon his arrest that he was a “national socialist” and a member of the group “Atom Waffen,” or “atomic weapon” in German.

Russell returned from U.S. Army National Guard duty Friday to find that his roommate had killed two men inside the Tampa apartment they shared, according to the Miami Herald.  His roommate, Devin Arthurs, was arrested Friday for the deaths of both men and for holding another three people hostage inside a nearby store. Arthurs, 18, was also a neo-Nazi until he converted to Islam and told police he was angered by the world’s “anti-Muslim” sentiments and “wanted to bring attention to his cause.” He said the two men he murdered were also neo-Nazis.

“This wouldn’t have happened if your country didn’t bomb my country,” he reportedly said, yelling “Allah Mohammed” while being led into the police car.

After being called to the hostage scene and arresting Arthurs, police located the bodies of Jeremy Himmelman, 22, and Andrew Oneschuk, 18, inside an apartment at the Hamptons Condominium complex. Both men appeared to have died of gunshot wounds to the head and chest. Police detective Kenneth Nightlinger said in the arrest report that Arthurs informed those who he was holding hostage “that he was upset due to America bombing his Muslim countries.”

At the time of Arthurs’ arrest police were concerned about the possible presence of explosives in the building. The Tampa Police bomb squad and the Tampa Fire Rescue Hazmat team were called to the complex where they worked “though the night” to ensure it was safe, though no explosives were ultimately found.

Arthurs quickly confessed to the murders, going so far as to detail the order in which he killed the men and the type of rifle he used. Police said they were attempting to determine what happened in the lead-up to the shooting.