BRUSSELS (Reuters) – Belgian investigators believe explosives used in the attacks in Paris in November may have been made in an apartment in Brussels that was rented under a false name and where a fingerprint of a key fugitive was found.

Police found material that could be used to make explosives, traces of explosive acetone peroxide and handmade belts during a raid on the apartment on Dec. 10, federal prosecutors said in a statement on Friday.

Belgian newspaper De Standaard, which reported the raid in its Friday edition, said the investigators believed the explosives were probably packed into suicide belts in a hotel outside Paris in the lead-up to the Nov. 13 attacks.

Prosecutors investigating Belgian links to the Paris attacks said the apartment in the district of Schaerbeek had been rented under a false name that might have been used by a person already in custody in connection with the Paris attacks.

The find adds to indications that the Nov. 13 shooting and suicide bomb attacks in Paris, in which 130 people were killed, were at least partially planned in Belgium.

Two of the attackers had been living in Brussels and Belgian authorities have arrested 10 people.

Investigators also found a fingerprint of Salah Abdeslam, the brother of one of the attackers, who returned from Paris the morning after the attacks and has still not been found.

Many of those arrested in Belgium have links to Abdeslam, including two who drove from Brussels hours after the attacks to pick him up and another who drove him from one part of Brussels to Schaerbeek after his return.

According to De Standaard, investigators believe the fingerprint indicates Abdeslam used the flat as a safe house after the attacks, given signs that the apartment had been partially cleaned up, although they do not know how long he stayed there.

Belgian media also said this week investigators also now believe that two men controlled the Nov. 13 attacks by sending SMS text messages from Belgium during the evening.

Prosecutors appealed to the public for help on Dec. 4 in the hunt for these two men who traveled with Abdeslam to Hungary in September using fake identity cards with the names Samir Bouzid and Soufiane Kayal. Grainy images of their faces are shown on the federal police’s website.

The two, clearly older than the attackers, are believe to have played a pivotal role, according to Belgian newspaper La Libre Belgique, in assuring logistics for the operation that was months in the planning.

The same false identity of Soufiane Kayal was used to rent a property in the Belgian town of Auvelais that possibly served as a safe house.

The other false identity card, for Samir Bouzid, was used four days after the attacks to transfer 750 euros at a Western Union office in Brussels to Hasna Aitboulahcen, who died in a police assault in St Denis on Nov. 18.

Separately, federal prosecutor Frederic Van Leeuw warned in an interview on broadcaster VTM late on Thursday that the Jan. 15 anniversary of a foiled attack on Belgian soil could prompt someone to launch an attack in the country.

“We know that they opt for symbolic dates although on the other hand no one knows why Charlie Hebdo took place on Jan. 7,” he said.

(Reporting By Philip Blenkinsop; Editing by Toby Chopra)