One of the two men responsible for carrying out Turkey’s deadliest terrorist attack Saturday owned a cafe where supporters of the Islamic State militant group, also known as ISIS, would often hang out, new reports indicate. The establishment was well-known to both Turkish authorities and the local and international media, which had been warning of potential dangers from the individuals involved for years, Bloomberg News reported Thursday. The news follows the revelation Wednesday that the man responsible, identified by Turkish media as Yunus Emre Alagoz, was the brother of the 20-year-old behind a deadly bomb blast in the southern Turkish city of Suruc in July.

"I find it hard to believe that these bombers, whose names and families were written about extensively in the press, were not being watched by the government and came to Ankara without the National Intelligence Agency knowing about it," Ezgi Basaran, a columnist at Radikal newspaper, told Bloomberg by e-mail. Radikal has reportedly covered the ISIS cell Alagoz belonged to since 2013.

Adiyaman, a small, mostly-Kurdish city in Turkey’s southeast, has produced a disproportionate number of ISIS sympathizers. Aside from the Alagoz brothers, friend Orhan Gonder was charged with bombing a left-wing Kurdish rally in June. The tea house Alagoz owned was reportedly shut down last year for operating without a license after pressure came from parents of those who attended the cafe.

Ankara Family members of Cemal Avsar, a victim of Saturday's Ankara bomb blasts, mourned over his coffin during his funeral in Istanbul, Oct. 12, 2015. Photo: Osman Orsal/Reuters

Alagoz’s alleged accomplice in Saturday’s bombing, Omer Deniz Dundar, was also reportedly on a list of 21 would-be suicide bombing suspects. Dundar's family members have complained of government failure to take action to prevent the attack.

"I went to the police countless times to try and get my son back from Syria," Dundar's father, identified only by the initials M.D., reportedly told Radikal Wednesday. "I told the police: ‘Please take him and throw him in jail.’ They took his statement and then let him go."

When a family member reportedly brought the issue up personally with the country’s prime minister, Ahmet Davutoglu, he allegedly responded: "It’s good that they went together, they’ll support each other," according to a field report authored by the opposition Republican People's Party.

Davutoglu said several days after Saturday’s blast that Turkey knew of potential threats, but could not act without evidence of a planned attack.

"We have a list of people who may carry out suicide bombings," Davutoglu said. "As a country with rule of law, you can’t arrest them until they act."