IE 11 is not supported. For an optimal experience visit our site on another browser.

BREAKING: CNN CEO Chris Licht is out at the network, drawing rocky tenure to a close

'Jihadi' John' Suspect Mohammed Emwazi Escaped Britain in Truck: Sources

The man believed to be the black-clad ISIS militant believed he was on a watch list and arranged his escape from Britain, sources said.

A man suspected to be the black-clad ISIS executioner known as "Jihadi John" believed he was on a watch list by authorities in Britain and escaped from the country in the back of a truck, according to U.K. security sources.

The security sources did not say when exactly Mohammed Emwazi, 26, left Britain and eventually made his way to Syria, but said once out of Britain he was able to travel across Europe and to the Greek-Turkish border unchallenged because of the Schengen Agreement, which did away with border checks across much of the continent.

Emwazi was unmasked last week as the ISIS executioner seen in some of the terror group’s gruesome execution videos. He'd disappeared after he was barred from travelling to Kuwait in 2013, and he turned up in Syria about four months later, the sources said.

Related: 'Jihadi John': New Recording of Mohammed Emwazi Emerges

The revelation that Emwazi may be "Jihadi John" underscores the difficulties faced by security services like MI5 in monitoring suspects who appear on the fringes of terror investigations, but do not become involved in planning attacks.

Emwazi first came to the attention of authorities in 2009, after security services learned he had been in contact had been in contact with one of the men convicted of attempting to bomb London's transit system on July 21 2005, two weeks after suicide attacks killed 52 commuters, and that he had also been in touch with others planning to join al Shabaab militants in Somalia, the sources said.

He was placed under surveillance, but after two and a half years passed with no evidence Emwazi became further involved in terrorism, he was re-classified as a “low-level subject of interest,” the sources said. Emwazi was on a watch list but it was unclear if he was on a “no fly list” — which would have prevented him from leaving the country — when he disappeared.

Sources said that monitoring low-level subjects of interest like Emwazi — whose names crop up during other investigations but aren’t suspected of planning terror attacks themselves — is one of security officials' "greatest challenges."

The Parliamentary Intelligence and Security Committee last year said MI5 did not have a strategy for dealing with the "cumulative effect" of such persons of interest. The security service told the committee that in 2012 and 2103 — the time Emwazi disappeared — it had "hundreds" of open investigations, and there were over 1,000 "subjects of interest" being investigated.

Related: Co-Worker Tells of 'Very Committed' Jihadi John

Emwazi had faced challenges in returning to Kuwait in the years before he disappeared. He was first deported from Tanzania in 2009 on suspicion he planned to join al Shabaab.

But he was able to travel to Kuwait shortly thereafter and lived there for about eight months, but upon his return to Britain was barred from returning to Kuwait because his visa had been withdrawn, the sources said. Emwazi was placed under surveillance for a time in 2011 and later became involved in a street gang.

In 2013, his father suggested Emwazi change his name in a bid to get back to Kuwait, the sources said, but it didn’t work. When that attempt failed, he disappeared and turned up in Syria, the sources said. Emwazi feared he was on a watch list, and sought help from associates who smuggled him out of the country through a Channel port, the sources said.

Emwazi’s father was reportedly horrified to learn his son may be "Jihadi John." Jasim Emwazi, a manager at a depot in Kuwait, cried and said “"May God … take revenge on him," a co-worker told NBC News this week. Mohammed Emwazi remains at large and is believed to be in Iraq or Syria. Lawyers for his family say there is no proof "Jihadi John" is Emwazi.

— Duncan Gardham contributed to this report