New York lawyer Stanley L Cohen has spent much of his career representing terror suspects — including Osama Bin Laden’s son-in-law — and has been labelled a “traitor” and an “enemy of Jews, Israel and America”.

But earlier this year, the Orthodox-raised attorney (pictured right) used his jihadi contacts in a vain attempt to try to save American aid worker Peter Kassig from being beheaded by Islamic State (IS).

After discussing his plan with the FBI, Mr Cohen asked two of al Qaida’s most prominent “spiritual guides” to help secure the release of Mr Kassig, who had reportedly converted to Islam while in captivity in Syria.

After flying to the Middle East on October 13, Mr Cohen drew up a “protocol” together with the Jordanian authorities and the FBI that would allow the clerics to begin talks with IS without fear of reprisals.

Within a few days, one of the clerics, Abu Mohammed al-Maqdisi, had begun to exchange messages with Turki al-Binali, IS’s chief scholar, over social media platform WhatsApp and, by October 26, Mr Cohen was confident that Mr Kassig would be freed.

But Mr Cohen’s efforts failed and Mr Kassig was beheaded in November. Mr Cohen said that Jordan scuppered the negotiations by breaking his “protocol” agreement and arresting al-Maqdisi for contacting al-Binali.

Mr Cohen said that he felt “sandbagged” by Jordanian and US officials. “This is why the whole thing went to s**t,” he said. “Jordan violated the protocol and the US failed to intervene to let al-Maqdisi go, which it could have done.

Mr Cohen had been prompted to help Mr Kassig after he received a call from Palestinian friends in Lebanon who had personally witnessed the hostage’s humanitarian work and were deeply troubled by his plight.

Mr Cohen had never undertaken such an operation before, but said he was moved to act. “I thought: ‘Can I save him?,’ ” and concluded it would be worth a serious try.

Aside from his track record defending terror suspects, the lawyer, 62, has been vilified by many fellow Jews for his leftist “radical” positions on Israel and for having friends among the top ranks of Hamas. His personal website even includes a section for his “haters”.

He said his Jewish identity has never been a factor in his interactions with Islamists or other alleged terrorists and had nothing to do with Mr Kassig’s ultimate fate.

“I’ve been dealing with Hamas, with Hizbollah, for many years behind the scenes,” he said. “They know me. They know who I am. People have trusted me.”

Mr Cohen, who defined himself as a, “non-religious spiritual Jew”, said he has many Jewish friends who vouch for his integrity, decency, and human empathy.

In January, he is due to start serving an 18-month sentence related to tax evasion charges brought by the Internal Revenue Service.