A Pakistani lawyer under death threats for defending a doctor who helped CIA agents hunt al-Qaida leader Osama bin Laden was shot dead on Tuesday, police said, and two militant groups claimed responsibility.

Samiullah Afridi represented Dr. Shakil Afridi, who was jailed in 2012 for 33 years for running a fake vaccination campaign believed to have helped the U.S. intelligence agency track down bin Laden. That sentence was overturned in 2013 and the doctor is now in jail awaiting a new trial.

Samiullah Afridi was shot dead on Tuesday as he was returning to his home in the northwestern city of Peshawar, police said. According to media, he had recently returned there from abroad after leaving Pakistan for his safety.