Armed police patrol at the Christmas market in Oberhausen, western Germany on December 23, 2016
Berlin (AFP) - Berlin's Christmas market truck rampage was the deadly jihadist attack Germany had long feared, as security services have warned of the growth of a shadowy Islamist scene.
Rarely a week has gone by in past years without the arrest of a radical preacher, an extremist backing the Islamic State or other extremist groups with money, arms or propaganda, or of a fighter returning from Syria or Iraq.
Germany's domestic security chief, Hans-Georg Maassen, has likened the rise in IS followers to a dangerous "youth subculture".
He said that while it has drawn some home-grown converts and many female recruits, the main target group has shared the "four Ms" profile -- male, Muslim, with a migrant background and a history of personal misadventure.
It is a profile that fits 24-year-old Tunisian Anis Amri, the Berlin attack suspect shot dead Friday by an Italian police officer in Milan.
An illegal migrant, drug dealer and ex-convict, he is seen in a video message pledging allegiance to IS chief Abu Bakr al-Baghdadi before he mowed a stolen truck through a Christmas market in an attack that left 12 dead.
It was the deadliest IS assault on German soil, but the country has already produced its share of extremist killers.
Perhaps Germany's most notorious IS fighter is Denis Cuspert, a German-Ghanaian former Berlin rapper known as Deso Dogg, who has appeared in an IS video with a man's severed head.
- Hate preachers -
In Germany, a leading alleged IS recruiter is Iraqi Ahmad Abdulaziz Abdullah A., also known as Abu Walaa or "the faceless preacher" for propaganda videos that showed him from behind.
Police in November arrested him and four others in Hildesheim -- a northern town with a reputation as an Islamist bastion, along with the capital and the industrial region of North Rhine-Westphalia.
After Monday's Berlin attack, it emerged that Amri had also been in contact with the "hate preacher", one of the leading voices of a movement that has grown sharply in recent years.
The domestic security service estimates that the number of radical Islamists in Germany rose above 9,000 this year, from some 3,800 in 2011.
About 550 are considered capable of a violent attack -- a list that included Amri.
This year, Germany has been shocked by a spate of attacks committed by young followers -- including some who were among the more than one million migrants and refugees who have arrived in the past two years.
In February, 15-year-old German-Moroccan girl Safia S., previously known for singing religious songs on YouTube, stabbed a police officer in the neck with a kitchen knife, wounding him badly.
In April, three 16-year-olds set off a bomb in Essen that left three people injured at a Sikh community wedding.
In July, a 17-year-old Afghan refugee wounded five people in an axe rampage on a train before police shot him dead.
Days later a 27-year-old rejected Syrian asylum seeker blew himself up outside a music festival, wounding 15 people. Both July attacks were claimed by IS.
The youngest plotter known so far is a 12-year-old German-Iraqi boy who tried to set off a home-made nailbomb in Ludwigshafen this month.
- 'Powerless' parents -
Peter Neumann, head of the International Centre for the Study of Radicalisation at King's College, London, said that for some very marginalised and troubled youths, IS represents "a kind of protest ideology, a counterculture".
Many small-time criminals are drawn to -- and share their skills with -- the IS "super gang", he told Berlin public radio, in the belief that it promises "might, weapons, adrenaline, adventure... and on top of that, salvation."
The parent of one of the youths in the Sikh temple attack, Turkish-born Neriman Yama, wrote about her son's radicalisation in the book "My Son, the Salafist", referring to a fundamentalist branch of Islam.
In it she describes how she watched her son Yusuf start watching Arabic preachers online at age 14, speak in verses, marry a teenage girl wearing a burqa, and eventually turn to violent jihadism.
She said that she sought help from mosques, police and security services, even getting Yusuf enrolled in an official deradicalisation programme, but could not prevent the attack.
"As parents, we were powerless," Yama told journalists. "The other side was stronger than us."