When Turkish businessman Yıldırım Demirören quit as the president of Istanbul football club Beşiktaş, on 27 February 2012, he left behind a legacy of destruction. The club’s finances were in dire condition, with €200 million in debt, an accumulated budget deficit of over €160 million, and a growing pile of unpaid bills. One of the great historic Istanbul teams, alongside Fenerbahçe and Galatasaray, Beşiktaş would soon receive its second ban from the UEFA Champions League and was deeply embroiled in a match-fixing scandal.

But the outgoing chief was not resigning in disgrace. In fact, his departure was necessitated by his appointment to a better job, as head of the Turkish Football Federation (TFF), the governing body of football in the country. He still occupies this post today.

Part of Beşiktaş’s financial woes stemmed from questionable transfer deals Demirören facilitated with players connected to the Irish football agency, Gestifute, run by Portuguese agent Jorge Mendes. In little over one year, mostly in a six month period, Demirören personally signed secret commission agreements with Gestifute that netted the world’s biggest agent €6 million in fees and cost the club over €60 million in transfers and player salaries.

The new investigation by The Black Sea, based on Football Leaks documents obtained by Der Spiegel and shared with the European Investigative Collaborations journalism network, reveals that Gestifute’s lucrative commission contracts with Beşiktaş were illegitimate and broke FIFA and Turkish Football Federation rules.

The documents show that when Mendes tried to recover €1.75 million in overdue payments from Beşiktaş, his Turkish lawyer informed him that “taking the dispute to FIFA was very risky” because the association would likely reject their validity.

Three separate lawyers and a money laundering expert consulted by The Black Sea confirmed that the appearance of Gestifute and the signature of the company’s tax accountant - who is not a licensed FIFA agent - rendered them improper and illegitimate.

The deals might also have broken FIFA and TFF rules on conflict of interest, since they were each of them private commission contracts arranged directly between the club and Gestifute, which was improperly acting as a player agent in the negotiations.

Also involved is Mendes’s Turkish associate, fellow superagent Ahmet Bulut, who could also be breaching Turkish Football Federation rules by failing to declare his role as an intermediary on at least eight of Mendes’s deals.