(CNN) -- German authorities have indicted 10 people in connection with a stampede at a music festival that killed 21 people in July 2010.
The deadly crush happened at the Love Parade festival in Duisburg.
Six city workers and four who worked for the event organizers were charged with involuntary manslaughter and bodily injury caused by negligence, a senior prosecutor said Wednesday.
The deadly crush took place between the main event site and an expansion area in an underpass that became a fateful bottleneck.
Faulty crowd flow planning led people both entering and exiting the festival to cram into the underpass from both ends, Michael Schwarz said in a prepared statement.
In addition, barriers that were installed without approval hemmed the crowd in, further increasing the congestion.
Witnesses told CNN affiliate NTV that the underpass became dangerously overcrowded, and some people who were crushed against the walls and each other lost consciousness.
That triggered a panic in the crowd, unleashing a stampede.
The Duisburg public prosecutor's office said 652 people were injured. Of them, 283 had to be treated in hospitals.
Masses of people attended the annual electronica and techno music festival, but there is much disagreement on the size of the crowd.
NTV said about 1.4 million people showed up at the Love Parade festival, which featured dozens of DJs spinning techno music for hours.
Organizers expected only 700,000 to 800,000 attendees, so to accommodate more people, they opened an additional event site.
But the numbers are disputed by police, who said that the area can hold between 250,000 and 350,000 people and that it was not filled to capacity.
At the time, NTV said 1,400 police officers were on hand to monitor the event; Detlef von Schmeling of the Duisburg police said more than 4,000 police officers provided security.
Witnesses told NTV that police were warned at least an hour before the incident that the underpass was becoming dangerously crowded. An additional entryway had been opened before the accident to relieve some of the pressure.
Immediately after the calamity, the Love Parade's organizers dissolved the festival, vowing never to put it on again.
CNN's Diana Magnay and Ben Brumfield contributed to this report.