The Houston Police on Saturday opened a criminal investigation into the stampede at American rapper Travis Scott’s concert, in which eight people aged between 14 and 27 were killed, Reuters reported.

The police said they had received unconfirmed reports that someone in the audience was injecting other people with drugs.

The stampede took place around 9.30 pm on Friday at Scott’s Astroworld music festival in Houston. As fans in the audience of about 50,000 surged toward the stage, some fell unconscious after suffering “medical issues” while others were injured, the police said. The show was halted by 10 pm and the festival was cancelled.

The police said that there were “a lot of narratives out there right now about alleged criminal behaviour in the audience”, The Guardian reported. One of the narratives pertained to an unidentified security officer at the concert claiming he felt a prick in his neck before falling unconscious.

City Police Chief Troy Finner said that the medical officials also pointed at the needle mark on the security officer’s neck.

“We do have a report of a security officer, according to the medical staff that was out and treated him last night, that he was reaching over to restrain a citizen and he felt a prick in his neck,” Finner said. “When he was examined he went unconscious. They administered Narcan [an opioid antidote].”

The police are waiting for autopsy reports to ascertain the reasons behind the death of the eight people, Reuters reported. They said some victims were trampled. Twenty-five people were taken to various hospitals following the stampede, with some suffering cardiac arrest.

“I’m sending investigators to the hospitals because we just don’t know,” Finner said, according to The New York Times. “We’re going to do an investigation and find out, because it’s not fair to producers, to anybody else involved, until we determine what happened, what caused the surge.”

Meanwhile, Scott posted a statement on Twitter, saying that the Houston Police had his “total support” in the inquiry.

“My prayers go out to the families and all those impacted by what happened at Astroworld Festival,” he wrote. “I am committed to working together with the Houston community to heal and support the families in need.”