Special Report - How Denmark's unexpected killer slipped through the net

COPENHAGEN (Reuters) - On Valentine's Day, two weeks after his release from prison, Omar Abdel Hamid El-Hussein walked up to a Copenhagen cafe hosting a debate on freedom of speech and sprayed it with bullets.

As a manhunt began, the 22-year-old went to ground. Nine hours later he launched a second assault, this time on a synagogue. Police eventually shot him dead, ending a rampage that left Danish filmmaker Finn Noergaard and security guard Dan Uzan dead, and six people wounded.

The attacks on Feb. 14 and 15 shocked Danes, who prize their country's openness and sense of security. The country was further confounded when it emerged that prison officials had warned Denmark's domestic intelligence agency that Hussein was at risk of being radicalised. If Denmark's prison system ? famed for its focus on rehabilitation and education over punishment ? could not prevent a young man from turning into an Islamist killer, then perhaps it was not the model that many Danes believe it was. Parliament demanded an inquiry into the attacks and how both the prison system and the municipality had handled Hussein's case.

In interviews with dozens of people, including a former cellmate and a source familiar with the as-yet unpublished official investigation, Reuters has learned new details about Hussein and his final months. His story seems to show how quickly people can be radicalised and how easily they can slip through the net, even a net as supportive and ostensibly secure as Denmark's.

Those who knew Hussein both inside prison and out say the son of Palestinian immigrants was a violent and troubled 22-year-old, but not a long-term convert to radical Islam. For most of his life he was a rebel without any obvious cause. He drank alcohol, listened to Katy Perry and did not appear very religious. 

Something changed in his final six months in prison, according to the source familiar with the official investigation. In September, according to the source, Hussein started talking about travelling to Syria. Two months later another young inmate who spent time with Hussein was found supporting extremist group Islamic State on social media using a hidden cell phone. Hussein was increasingly religiously observant, according to the source, and attacked another inmate just weeks before his release. 

Such rapid transformations are becoming more common, according to Matthew Levitt, a counter-terrorism and radicalisation expert at the Washington Institute for Near East Policy. Levitt, who last month served as a prosecution witness at the trial of Boston marathon bomber Dzhokhar Tsarnaev, said that the rise of Islamic State means "the pace of radicalisation has gone into hyper-drive. It is no longer a matter of months but of weeks or even days." Islamic State's use of social media and the Internet, he said, allows people to quickly learn its extremist doctrines without needing long exposure to its supporters ? in prison or elsewhere.

Much is still unknown. Police have arrested five other men. Lawyers say they face a range of charges including suspicion of procuring the weapons and bulletproof vest used by Hussein, and hiding evidence between the two shootings. At the same time, the Danish police have said that there is no indication Hussein was part of a cell or had travelled to Syria or Iraq. Police declined to comment for this story.