ESSEN (Germany) • The package ordered online arrived at his apartment on a Saturday morning - a cardboard box packed with magnesium, potassium nitrate and aluminium powder for a homemade bomb.
Weeks ahead of the attack, the terrorist cell's leader, called the Emir (a Muslim title for an exalted leader) by his comrades, had issued precautionary orders, said police.
"Delete ALL pictures and videos of the Islamic State," the Emir warned via WhatsApp, referring to the Islamic State in Iraq and Syria (ISIS) extremist group.
"Everything that is weapon-like or similar (also bombs) must be immediately disposed of... Sell it, give it away, move it or destroy it."
Then, one night last April, officials said, the Emir led two cell members to a Sikh house of worship in the German industrial city of Essen and hurled the bomb towards its door.
TARGETING DRIVE INTENSIFIES
The amount of Islamic State videos and propaganda aimed at children has jumped in recent months...
We haven't seen anything quite like this, not on this scale and of this quality. They know that, in the West, you don't expect a 10-year-old to be a terror suspect.
MR DANIEL KOEHLER, director of the German Institute on Radicalisation and Deradicalisation Studies.
A deafening boom rang out. Orange flames lit a mosaic of blood and shattered glass. Inside, victims screamed as the assailants fled.
All three of the terrorists were 16-year-old boys, said the German police.
The threat presented by ISIS is taking on a new form: child terrorists in contact with or inspired by the group. Even as it suffers setbacks on the battlefield in Iraq and Syria, ISIS is cultivating adolescents in the West, who are being asked to stay in their home countries and strike targets with all available weapons, including knives and crude bombs.
"The amount of Islamic State videos and propaganda aimed at children has jumped in recent months," said Mr Daniel Koehler, director of the German Institute on Radicalisation and Deradicalisation Studies.
"We haven't seen anything quite like this, not on this scale and of this quality. They know that, in the West, you don't expect a 10-year-old to be a terror suspect."
The French authorities said last Friday that a 16-year-old girl was among four people arrested in the south of France on suspicion of planning a terrorist attack.
Last December, a 12-year-old German Iraqi boy - guided by an ISIS contact in the Middle East who addressed him warmly as "brother" and groomed him via the encrypted messaging app Telegram - built and tried to detonate a bomb near a shopping centre in the western German city of Ludwigshafen. The device failed to explode.
The boy had been "headhunted" by ISIS, said officials, after searching radical websites online. A 17-year-old accomplice was later arrested in Austria.
Last month, a 15-year-old girl - the daughter of a German convert to Islam and a Moroccan mother - was sentenced to six years in jail for an attack in February last year on a German police officer in Hanover. She gouged him in the neck with a kitchen knife, causing life-threatening injuries, after having been befriended and cajoled by an ISIS instructor via a text messaging service.
In Germany, at least 10 minors have been involved in five plots over the past 12 months. Unfortunately, the authorities said, the intelligence community is often blind to the threat posed by such teens and pre-teens.
Officials lack the legal authority to track children the same way they monitor adults, creating what the German authorities describe as one of their greatest counter-terrorism challenges. Intelligence agencies here have identified at least 120 minors who have become dangerously radicalised - and some of them cannot be intensely monitored because of domestic laws protecting children, said officials.
German law was amended last year to allow the collection of data on suspects as young as 14. But officials now argue that this is not young enough.
"We are allowed to monitor minors and record them in our databases in exceptional cases only, but they have to be aged 14 or over," said Mr Hans-Georg Maassen, who heads Germany's domestic intelligence agency.
"Normally, people do not expect children to commit terrorist attacks. But they can and are.
"What is really worrying is that people frequently look the other way. They say it's just a phase of adolescence and that surely they will grow out of it. Often, parents don't really know what their children are doing in their rooms."