ISTANBUL — According to state media reports, an American citizen of Turkish origin faces 15 years in prison after he surrendered to Turkish authorities last month over his role in founding a messaging app state officials say was used by supporters of a failed coup in 2016.

David Keynes, the alleged license holder for the ByLock app, reportedly turned himself in to Turkish authorities after arriving at Istanbul’s main airport on June 9, though news of his legal proceedings was initially made public Wednesday.

This comes after the Istanbul Chief Public Prosecutor’s Office on Dec. 17, 2020, issued a detention warrant for Keynes, a Turkish national formerly known as Alpaslan Demir who changed his name upon taking US citizenship in 2011.

Keynes was charged with “membership in an armed terrorist organization.” On March 4, 2021, his lawyer told authorities he would testify under Turkish remorse provisions that grant suspects more lenient sentences in exchange for collaborating with investigators. Legal experts familiar with the matter said information shared by Keynes in his testimony could impact future prosecutions involving suspects facing coup-linked charges.