Ahmed al-Shayea was known as the "living suicide bomb" – the young Saudi driver of a fuel tanker bomb in Iraq who survived to renounce violence and warn his countrymen of the dangers of jihad.

In the process he became Saudi Arabia's poster boy for a high-profile jihadi de-programming initiative whose secondary purpose is to discourage Saudis from joining al-Qaida.

With his burned face and mangled hands, Shayea was presented as a vivid warning to young Saudis about the perils of jihad and the untrustworthiness of al-Qaida, which he claimed had tricked him into driving the tanker bomb, which killed 12 people in 2004.

That was until November. Then Shayea disappeared from Saudi Arabia, only to reappear reportedly in Syria where – his Twitter feed reveals – he has rejoined the ranks of an al-Qaida franchise, the Islamic State of Iraq and the Levant (ISIL), which is engaged in a civil war with other rebels fighting the Assad regime.

The case of Shayea raises questions about the effectiveness of the jihadi de-programming efforts, including the well-known Saudi model, which has boasted of rehabilitating and releasing several thousand former jihadis, including some returned by the US.

And Shayea is not the only prominent jihadi to have returned to al-Qaida. Despite long denials of any recidivism, four years ago it was revealed that Said Ali al-Shihri, a former inmate of Guantánamo who was also released to the Saudis under the same programme, had re-emerged as al-Qaida's deputy leader in Yemen, one of a number of graduates of the de-radicalisation programme to return to the group.

Khalid al-Suwid, who also fought in Iraq and was released under the same programme in 2012, is another who quickly resumed jihad. His death in Syria was announced in a martyrdom video on Facebook.

Hundreds of young Saudis have undergone the jihadi de-programming, being re-educated in prisons and rehabilitation centres, a scheme run by the interior ministry and available only to captured jihadis who demonstrate a desire to revoke their beliefs.

If Shayea's story is instructive, it is because so much is known about him. Held by US forces in Abu Ghraib prison in Iraq after the fuel tanker attack, he was repatriated to Ha'ir prison in Riyadh, where he told a visiting cleric he had experienced a change of heart.

In an outreach programme similar to ones run in Egypt and Yemen at the time involving psychiatrists and clerics, Shayea was persuaded to go public, appearing on television as part of a co-ordinated campaign to persuade others not to follow him.

He had been tricked, he said in his appearances. Although he had gone to fight Americans, he added, he was not told that the tanker he drove into Baghdad was a bomb.

His message was not just aimed at Saudi Arabia's jihadis; the authorities were keen to show him off to the wider world as well. In 2007 he described rejection of jihad in an interview organised by the Saudi government with western media outlets. "I realised that all along I was wrong," Shayea told the Associated Press in a two-hour interview at a Riyadh hotel before returning to an interior ministry compound that serves as a sort of halfway house for ex-jihadis rejoining Saudi society. "There is no jihad. We are just instruments of death," he said.

When he was recruited in his home town of Buraida, Shayea was 19 and jobless. "My friend started telling me about Iraq, how Muslims are getting killed there and how we should go there for jihad," said Shayea in 2007. "He told me there were fatwas and DVDs issued by Saudi and Iraqi clergymen that called for jihad."

In another interview in the same year that was broadcast by Fox News, Shayea added: "I would like to say to the American people that Islam forbids killing innocent people."

What is puzzling about Shayea's return to al-Qaida in Syria is that – by his own account – while being treated by US forces in Iraq who had saved his life, he claims that he told his American interrogators where to find a senior al-Qaida figure in Baghdad and revealed all that he knew about the group.

Noman Benotman, president of the thinktank Quilliam, which has its own de-radicalisation work, believes that, of 4,000 to 6,000 Saudis who have gone through the scheme, only 80 to 100 have either picked up arms again or drifted back into jihadi ideology.

"You have to separate the myth from the reality of this programme. It has been largely successful, but it has not – as the Saudis have tried to claim in the past – been magic, with no cases of people returning to jihad.

"Some have gone to Syria, others to Yemen, but it is still a small number," said Benotman.

He said that graduates from the de-programming initiative had been influenced by the same narrative of the war in Syria as wider Saudi society, where Salafists have used the official attitude of the ruling family to argue that the royal family has been hypocritical over events in Syria.