City officials were being criticized almost immediately because they had restricted entry to only ONE path that created a choke point. People were still moving forward even though the entrance at the other end of the tunnel had been closed. This lead to a mass panic and chaos as fans were unsure where to go in the claustrophobic environment. The stampede started around 5 p.m. local time, shortly after police closed the tunnel because the festival grounds were too full. Police told those in the tunnel over loudspeakers to turn around and walk out from the direction they came.
German police union leader Rainer Wendt said in an interview on the Bild newspaper's web site that he warned Love Parade organizers more than a year ago that Duisburg was "too narrow, too small to handle this mass of people."
More pictures of the aftermath here:
The Wall Street Times news article here:
Yahoo! News groups article here: http://news.yahoo.com/s/ap/eu_germany_love_parade_deaths
To learn more about effective event planning and crow control issues ther are some great resources. The International Association of Assembly Managers (IAAM) (http://www.iaam.org/) regularly discusses this topic as a key component of event planning and security.
A company that focuses on this issue is Crowd Management Strategies (http://www.crowdsafe.com/) an their web site has a wealth of information and [sometimes gruesome] statistics.