A Turkish-born American linked to a messaging app used by organizers of a failed coup in 2016 has arrived in Istanbul and turned himself in to the police, state media reported on Wednesday.

David Keynes, also known in Turkey as Alpaslan Demir, holds the copyright to ByLock, an encrypted messaging app that has been banned in Turkey and across parts of the Middle East.

Ankara outlawed Bylock in the aftermath of the coup, saying US-based Muslim cleric Fethullah Gulen’s followers had used it to communicate on the night of the putsch that claimed the lives of some 250 people when a group of rogue soldiers attempted to overthrow the government.

It was followed by a sweeping political crackdown and mass arrests.

The Anadolu state news agency said Keynes arrived in Istanbul on June 9 and turned himself in to the police under a “repentance law” that grants more lenient treatment to people who confess to crimes.

It was not clear why state media reported Keynes’s arrest more than a month after his arrival in Turkey or why he had decided to turn himself in.

Anadolu said he was put in pre-trial detention and charged with terror-related offences that could see him jailed for up to 15 years.

Citing an indictment, Anadolu said Keynes had provided names of individuals, as well as details about Bylock.

Ankara blames the coup attempt on Gulen, who was an ally-turned-opponent of Turkish President Recep Tayyip Erdogan.

The Turkish leader responded to the failed putsch by ordering a comprehensive crackdown that officials say saw more than 321,000 people detained.

Most have been released, but the scale of the detentions has had a chilling effect on Turkish politics, leading to the detention of Erdogan’s political opponents and shutdown of independent media.

The courts have handed down life sentences to 3,000 people, according to Anadolu, while 4,890 defendants have been convicted over links to the coup bid.

Rights groups and Turkey’s Western allies have voiced alarm over the crackdown, saying President Tayyip Erdogan has used the abortive coup as a pretext to quash dissent. The government has said the security measures were necessary due to the gravity of the threat Turkey faces.