isis belgium
Belgian special forces police block a street in central Verviers, a town between Liege and the German border, in the east of Belgium, Jan. 15, 2015, after a raid on alleged extremists. Reuters/Francois Lenoir

When Belgian authorities raided the home of a man with alleged ties to the Islamic State group in November, they discovered a film that immediately sparked alarm. The footage appeared to show that extremists were using video surveillance to spy on the Brussels home of a senior researcher at a Belgian nuclear facility.

Authorities have speculated that supporters of the extremist group, also known as ISIS, were trying to get their hands on nuclear material, possibly by kidnapping the man or one of his family members, a report by the Center for Public Integrity said Monday. That material could then be used to create a radioactive "dirty bomb," potentially inflicting massive casualties on a major European city.

William H. Tobey, a former deputy administrator at the National Nuclear Security Administration, said: “The potential for a bad outcome when you have ISIS looking at nuclear people is substantial,” according to the report.

Radioisotopes, produced at the Belgian nuclear center, can cause radiation poisoning and sickness. The raid on the apartment, rented by Mohamed Bakkali, came just weeks after ISIS supporters Nov. 13 launched a series of attacks in Paris, resulting in 130 deaths. Authorities continue to investigate what Bakkali planned to do with the videos. Officials have long feared ISIS getting its hands on such material.

“We know that it would not require a team of nuclear physicists or even a particularly sophisticated criminal network to turn raw material into a deadly weapon,” an internal Energy Department report on the threat, designated for “official use only,” said in May 2013. “In many cases, a determined lone wolf or a disgruntled insider is all it might take.”

Materials that could be used to build a dirty bomb are stored at more than 13,000 buildings around the world. The questionable security status of many of the centers has caused alarm among security analysts and officials.

Hundreds of Belgian nationals have traveled to fight alongside ISIS in Syria and Iraq. Security experts remain concerned over returning radicals and homegrown extremists.