New details show the arrest in Bulgaria of a French citizen with ties to the attack on the Charlie Hebdo satirical newspaper in Paris followed a tip from his sister.

The arrest warrant issued by a French court for Mourad Hamyd was based on his sister Khadija’s report to police that her brother had boarded a train across Europe to Bulgaria, even though he had told her he would travel to Morocco.

The warrant, which was made available to the AP on Tuesday, said: “This route corresponds with the route that is usually chosen by the jihadist volunteers that want to join the Islamic State group in Syria or Iraq.”

Hamyd is the brother-in-law of one of the men who attacked Charlie Hebdo.