Police in Houston, Texas, have opened a criminal investigation into the deaths at the Astroworld festival on Friday.
At least eight people died and scores of people were hurt after a crowd surge on the opening night of the music event in Houston, Texas.
The victims were aged between 14 and 27. The identities of some of them are expected to be released on Sunday
Police are also investigating reports that somebody in the audience had been injecting people with drugs.
The incident began around 21:15 on Friday (02:15 GMT Saturday) when panic broke out as the crowd began to press towards the front of the stage during the rapper Travis Scott’s headline set.
As the crush began causing injuries to people, panic grew and the casualties quickly overwhelmed the on-site first aiders, officials said. Some 300 people were treated for injuries such as cuts and bruises.
The police investigation into the tragedy will involve the homicide and narcotics divisions, and will review video from the scene to explore the causes of the surge and what had prevented people from being able to escape.
Several concert goers had to be revived with the anti-drug overdose medicine, including a security officer who police said appeared to have an injection mark.
“We do have a report of a security officer… that he was reaching over to restrain or grab a citizen and he felt a prick in his neck,” Houston Police Chief Troy Finner said.
“When he was examined he went unconscious,” he added. “He was revived and the medical staff did notice a prick that was similar to a prick that you would get if somebody is trying to inject.”