Police and the mayor of a sleepy Dutch town "failed" in their handling of a riot triggered when thousands attended a party after receiving a Facebook invitation meant to be private, a probe found Friday.
Some 4,000 revellers descended onto the northern town of Haren in September after a local girl accidentally posted a public invitation for her 16th birthday party on the social network.
The soiree descended into chaos, with party-goers pelting police officers with rocks, bottles, flower pots and even bicycles, shops looted and chairs set on fire throughout the night.
"Right from the start authorities had no grip on the problem, there was no clear strategy to deal with it and what they did was insufficient," said Job Cohen, who chaired a five-person commission to investigate the so-called "Project X" riots.
Haren's mayor Rob Bats "did not make proper use of his competency to use all means at his disposal" to control the rampaging youths, many of whom travelled by train to converge on the quiet neighbourhood, he added.
"If this was a test for the police, you would have to come to the conclusion that they failed."
By the end of the night of violence, at least 29 people had been hurt -- including three officers -- 108 were subsequently arrested and damages ran into the hundreds-of-thousands of euros.
Images of bonfires and blood streaming from the heads of youths after running battles with riot police shocked the Netherlands, better known for its tolerance and non-violent culture.
Youths had started arriving in Haren early in the afternoon, many of them carrying alcohol and some drugs, Cohen explained.
Officials had prepared for trouble by blocking access to the girl's street, banning alcohol consumption near her home and having the teenager herself quit the premises.
But riot police had to intervene when a couple of hundred drunken youths tried to get into the street.
After pelting the police with missiles as they tried to force their way into the street, groups of rioters moved on to the centre of the town where they wrecked cars, fencing, street lamps and signs.
Some of the party-goers wore T-shirts bearing the words "Project X Haren", an allusion to the 2012 US teen film "Project X" -- about a suburban birthday party that gets out of control after an invitation goes viral.
As Amsterdam's mayor between 2001-10, Cohen has been widely credited for his open-minded and progressive approach to law and order in the capital.