Who is to blame for the deaths of nine people at the Astroworld Festival last Friday? Houston police have opened a criminal investigation and concertgoers have already filed more than 20 lawsuits against the event organizers and rapper Travis Scott, who continued to perform for more than half an hour after officials declared a mass casualty event.

Crowd safety expert Keith Still explains the science behind how a concert crowd can transform into an uncontrollable mass that threatens human life.

Houston Chronicle music critic Joey Guerra, who attended the festival, grapples with how music fans are processing the tragedy.

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