Former Guantánamo prisoner Mozzam Begg has said he offered to help secure the release of British hostage Alan Henning, who was executed by Islamic State militants last week. Begg, who heads the prisoner advocacy group Cage, spent three years in U.S. custody without charge or trial and was recently rearrested and held for seven months on terrorism charges in Britain. He was released after the case against him collapsed. Before his arrest, Begg had begun talks with the U.K. Foreign Office over helping to secure the release of Henning, a taxi driver who was on an aid mission in Syria. Begg told the BBC he wanted to send a video message he believed the militants would heed.

Moazzam Begg: “If I could make a video message, deliver it in the language, the terminology, the wording that Islamic State would understand, to say that I myself was a former Guantánamo prisoner dressed in orange or facing execution possibly because the Americans had built the execution chambers, Abu Bakr al-Baghdadi himself had been a prisoner of the Americans, so it was a very heartfelt, very direct statement that I wanted to make in the Arabic language.”

Begg said he had spent time in Syria before the rise of ISIS and secured the release of other hostages. He said the British government failed to look at his offers seriously due to “its attempt to demonize and criminalize me.”