ANKARA, Turkey (AP) — A Turkish-born American believed to be behind a secret messaging application that has been linked to Turkey’s failed 2016 military coup arrived in Istanbul last month where he turned himself in to authorities, the state-run news agency reported Wednesday.

Anadolu Agency said David Keynes, the alleged license holder for the ByLock messaging app who was wanted in Turkey, was taken into police custody at Istanbul’s main airport on June 9.

Turkish authorities say the ByLock app was used by members of the network led by U.S.-based Muslim cleric Fethullah Gulen, who is accused of orchestrating the coup. The application has been used as evidence in Turkish courts against alleged perpetrators of the failed attempt.

Keynes' surrender came months after he declared through his lawyers that he wanted to cooperate with the Turkish authorities under a “repentance law” that grants offenders more lenient punishments, Anadolu reported.

The agency said Keynes has since been charged with membership in a terror organization and faces a maximum 15-year prison term. No trial date has been set.

On July 15, 2016, factions within the Turkish military used tanks, warplanes and helicopters in an attempt to overthrow President Recep Tayyip Erdogan’s government. Heeding a call by the president, thousands took to the streets to stop the coup. A total of 251 people were killed and around 2,200 others were wounded. Around 35 alleged coup plotters were also killed.

Gulen, a former Erdogan ally who lives in Pennsylvania, denies involvement in the coup attempt.

Turkey has designated his network a terror group, which it has named the Fethullahist Terror Organization, or FETO.

The government declared a state of emergency after the failed coup and launched a massive crackdown on the network.

Around 4,900 people have since been sentenced to prison, including around 3,000 who were given life sentences. More than 130,000 people were fired from public service jobs, including more than 20,000 military personnel.