Police have arrested Etem Taş, a senior figure of the Gülenist Terror Group (FETÖ), in Istanbul on April 30 after a six-month surveillance operation.

Taş was in charge of the group's members in 14 cities and was among names who went into hiding after FETÖ launched an unsuccessful coup on July 15, 2016. He was staying in gaybubet (absence) houses, a type of safe house used by the group to hide its members in Turkey. Officials also said that he was using an untraceable phone for communications.

Police captured him when he was meeting his wife at a park in Istanbul's Acıbadem neighborhood. They discovered that he had an encrypted messaging app in his phone used for communications with FETÖ's other senior figures.

The suspect had close ties to Fetullah Gülen, the leader of FETÖ, and repeatedly visited him in his retreat in the U.S. state of Pennsylvania.

Investigations unearthed his encrypted online correspondence with Mehmet Yaşa, a New York-based FETÖ figure, Mustafa Yeşil, a Brussels-based senior FETÖ figure and İsmail Cingöz, head of the now-defunct charity Kimse Yok Mu, which was used to funnel money to the terrorist group.

Since December 2013, when the terrorist group emerged as the perpetrator of two coup attempts, FETÖ has been regarded as a security threat. Prosecutors claim that the group's infiltrators in law enforcement, the judiciary, bureaucracy and the military had waged a long-running campaign to topple the government. The group is also implicated in a string of cases related to its alleged plots to imprison its critics, money laundering, fraud and forgery. As its activities face heightened scrutiny following multiple attempts to seize power, FETÖ apparently strove to hide its fugitive followers, according to its former followers. A former member who testified to prosecutors said that the number of the group's gaybubet houses increased from 75 to 560 across Turkey. Authorities believe that number might be even higher.