ANKARA, Turkey (AP) — A Turkish official says authorities are working to understand how a former British officer who helped found the White Helmets volunteer aid group in Syria died.

James Le Mesurier was found dead near his home in Istanbul on Monday. Turkish police believe he fell to his death and are investigating the circumstances.

Istanbul governor Ali Yerlikaya told reporters Tuesday: "Our chief prosecutor's office, our police are engaged in multifaceted efforts to shed light on the incident."

Le Mesurier was the founder and CEO of May Day Rescue, which established and trained the White Helmets, also known as the Syria Civil Defense, a group of local humanitarian volunteers.

Turkey's state-run Anadolu Agency reported he was 48 and had moved to Turkey with his wife four years ago.