Houston mayor Sylvester Turner has promised a “thorough review and investigation” of the tragedy at the Travis Scott-headlined festival in the city, where eight people died and more than 300 were injured as crowds surged and stampeded during Scott’s set. Approximately 11 people suffered cardiac arrest at the show, Turner said, although causes of death are under review.

“We had more security over there than we had at the World Series games,” Turner told the New York Times on Saturday, noting that the event took place on county property, with security organized by the city of Houston. City police provided hundreds of officers, “in addition to what I’m told were 240 or 250 non-police security that were there,” he said.

However, reports on social media and a Variety eyewitness said that a largel number of people attempted to rush the gates in order to gain entry without tickets, both during the afternoon and before Scott’s set. Multiple accounts also said that concertgoers had a difficult time finding or notifying security of the situation.

Turner added that it was too early to determine whether security precautions were sufficient. “I’m going to hold any sort of conclusion pending a thorough review and investigation,” he said.

A source told Variety that organizers suspected spiked drugs had caused the cardiac arrests, but Turner cautioned against speculation.

“I don’t even want to go to drug overdoses,” he said. “We are looking at all potential causes of this incident or what caused the cardiac arrest. We’re not taking anything off the table.” He said the ages of the dead, whose names have not yet been released, were between 16 and 23.

He added that preliminary reports suggested that most of the injuries occurred “in one particular area. This was not all throughout the front part of the staging area.”

Turner told the Times that he has longstanding connections to Scott’s family. “I’ve worked with the family, I’ve worked with Travis, I’ve worked with his mom,” he said. “This is a tragic case and that’s why I want a very, very thorough investigation of this.” He said he had not yet spoken with Scott.