Eight people died and hundreds more were injured after a crowd surge on the opening night of the Astroworld festival.
The victims were aged between 14 and 27. Some of their names have started to be openly announced.
Police are additionally looking into the real possibility that a person in the audience was injecting people with drugs.
Panic ensued after the crowd began to press towards the front of the stage during the rapper Travis Scott’s headline set. It began around 21:15 on Friday (13:15 AEST Saturday)
Panic grew as festival goers started getting injured, and the casualties swiftly overwhelmed the on-site first aiders, officials said. Around 300 people were treated for injuries such as cuts and bruises.
Both the homicide and narcotics divisions of the police will be involved in the investigation and will examine video footage from the scene to establish the cause of the surge and to understand what prevented people from escaping.
Numerous people had to be revived with anti-drug overdose medicine, including a security officer who police said appeared to have an injection mark on his neck.
“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.”