VIENNA (Reuters) - A Tunisian man suspected of killing an elderly couple in their home is believed to have had an Islamist motive, Austria’s Interior Minister Wolfgang Sobotka said.

The killer slit the throat of an 85-year-old woman with a knife and stabbed and beat her 87-year-old husband in the northern city of Linz on Friday. He also brought fuel and set fire to their flat.

Investigators who searched the suspect’s home and looked at his social media activities found that the killing “clearly had an Islamist background”, ORF radio on Thursday quoted Sobotka as saying late on Wednesday.

“It turns out that the suspect is obviously a radicalized Muslim who has murdered two people,” Sobotka said. “For this reason I am talking about a murder case which clearly has an Islamist background.”

The suspect, a 54-year-old Tunisian who has been living in Austria for 28 years, knew the victims. He used to deliver their groceries and allegedly believed the couple had links to the far right.

“He said he committed the murders for political motives and out of hatred of the FPO,” a police spokesman said, referring to Austria’s far-right Freedom Party.

When asked whether the suspect, who handed himself to police, also mentioned Islamist motives, the spokesman declined to comment.

Current evidence suggested that the suspect acted alone and not within a network, Andreas Pilsl, Upper Austria’s chief of police, told the radio.

He said intelligence services had looked into the suspect in 2015 following anonymous tips but “nothing was found that could indicate a radicalization”.

An attack at the Berlin Christmas market in December which killed 12 people, was carried out by a Tunisian.

Austria’s federal office for the protection of the constitution said in a recent report that religiously motivated Islamic extremism and terrorism were the biggest threats to internal security.

Several of the deadly recent Islamist attacks in France, Britain, Germany and Belgium have been carried out by “lone wolf” assailants with little apparent connection with militant networks.