French police interrogated one suspect and searched for others on Sunday, after a Greek Orthodox priest was shot and critically wounded while closing the door to his church in the city of Lyon.

Investigators are trying to determine whether a man arrested on Saturday night was the gunman behind the attack, or has information about it, according to a police official.

The priest remains in critical condition after being shot with a hunting rifle.

The motive for Saturday’s shooting remains unclear. Anti-terrorism prosecutors are not investigating the case, and the Lyon prosecutor has opened an attempted murder investigation.

The attack came as France is under high security alert after the killing of three people at a Nice church on Thursday, amid global tensions over cartoons of the Muslim Prophet Mohammed published in a French newspaper. The French prime minister has promised more protection for religious sites.

It also came amid tensions within the Greek Orthodox community in Lyon. The priest, a Greek citizen, had had a long-running legal dispute with a former monk who was convicted of defamation, according to French media reports.

The Greek Orthodox Holy Diocese of France identified the victim as Father Nikolaos Kakavelakis, and said he was scheduled to return to Greece after his time working at the Lyon church. “We pray for a speedy recovery and unequivocally condemn all forms of violence,” it said.

Antoine Callot, the pastor at another Greek Orthodox church in Lyon, told the Associated Press that the Greek Orthodox community in Lyon has not received any threats, but added he immediately asked police for security protection at his church after the shooting.