I don't believe they actually been convicted or anything like that. I think he means there's evidence of funding. There's also evidence of the Turkish government allowing ISIS to transport troops/supplies/recruits through Turkey to Syria.
From WSJ: "The ISIS crisis in Iraq is inextricably tied to the dangerous and permissive border policies of Mr. Erdoğan's government in Turkey over the past two years. It was only last year that U.S. President Barack Obama chided Mr. Erdoğan for "letting arms and fighters flow into Syria indiscriminately and sometimes to the wrong rebels, including anti-Western jihadists."
Mr. Obama wasn't alone in that assessment. As Human Rights Watch noted in an October report, "Many foreign fighters operating in northern Syria gain access to Syria via Turkey, from which they also smuggle their weapons, obtain money and other supplies, and sometimes retreat to for medical treatment."
Mr. Erdoğan has denied these allegations and vowed to prevent aid from flowing to jihadists in Syria. But media and law-enforcement reports contradict his statements. "The relative accessibility of the Syrian-Turkish border explains" why so many jihadists have made their way to Syria, the Journal reported earlier this month, citing Europol.
ISIS has found other transit points into Syria. But it's clear that this group, and other violent factions, have benefited from Turkey's Wild Wild East. As Thomas Hegghammer of the Norwegian Defense Research Establishment told the website Syria Deeply in December, "Turkey is to Syria now what Pakistan was to Afghanistan in the 1990s." - http://www.wsj.com/articles/how-turkey-is-exacerbating-the-mideast-crisis-1403722487