HOUSTON (AP) — The deaths of eight people in a crush of fans at a music festival have led to calls for an independent, outside investigation instead of one by the Houston police, who along with the fire department played a key role in crowd control and other safety measures at the show.

Experts in crowd safety say an investigation by neutral outsiders into the tragedy during Friday night’s performance by rapper Travis Scott could help the city avoid potential conflicts of interest and promote transparency.

Houston Police Department spokeswoman Jodi Silva declined to comment on whether the department’s close involvement in the event created a conflict or if it was considering handing the probe off to an outside agency. Such decisions are often made in investigations like police shootings.

“All of the information we have available to put out at this time has been placed out on Twitter,” Silva said.

The police department’s probe would be separate from any independent investigation ordered by County Judge Lina Hidalgo, Harris County’s top elected official, according to Rafael Lemaitre, a spokesman for the county judge’s office. Hidalgo hasn’t decided who would conduct such an independent review or how it would be done, Lemaitre said Monday.

“She wants to know if this could have been prevented in any way,” Lemaitre said. “It’s also entirely possible that it was not preventable for whatever reason, and that’s something we would like to know, as well.”

Key questions remain unanswered after the Astroworld festival at the Harris County-owned NRG Park. Some involve what the Houston police and fire departments did before, during and after a crowd surged toward the stage, killing eight people and injuring many more, with over 300 people treated on site and at least 13 others hospitalized. Other questions center on the actions of event organizers.

Officials with the Houston police and fire departments have said that part of their investigation will include reviewing whether the concert promoter and others behind the festival adhered to the plans that were submitted for the event.

Astroworld’s organizers laid out security and emergency medical response protocols for the festival in plans filed with Harris County. The 56-page plan, obtained by The Associated Press, says any decision to evacuate the event would be made by the festival director after consultation with other individuals, including the security director. Such plans have to be reviewed by Houston police officials.

Christopher Slobogin, director of the criminal justice program at Vanderbilt University, said an independent criminal investigation could be beneficial to avoid any potential conflicts of interest, but acknowledged this case is different from typical situations where authorities are confronted with decisions over whether to step away from a case.

“The actual crime was probably not committed directly by the fire department or the police department,” he said. “But at least for appearance purposes, if an independent body did the investigation I think that would be the better practice.”

Officials have said a private company was primarily responsible for providing security at the festival, but Houston police were also assigned to the event. The plan says medical care at the festival was provided by ParaDocs, a private company based in New York.

Houston Fire Chief Samuel Peña said during a news conference Saturday that the injuries and size of the crowd “quickly overwhelmed” the private companies providing security and medical services. Peña said even though the medical operations plan did not require the fire department to have units pre-positioned around the festival, those units were in place “in case this incident escalated.”

Houston Police Chief Troy Finner said in a statement on Monday that he had a “brief and respectful” meeting with Scott and the rapper’s head of security on Friday before his performance. The chief said he asked them to work with the police department.

“I expressed my concerns regarding public safety and that in my 31 years in law enforcement experience I have never seen a time with more challenges facing citizens of all ages, to include a global pandemic and social tension throughout the nation,” Finner said.

G. Keith Still, a visiting professor of crowd science at the United Kingdom’s University of Suffolk, said his independent investigations of similar tragedies typically begin with evaluating an event’s safety permit process, including how a permit was issued and whether the event organizer adhered to permit conditions.

“Police can sometimes get too caught up in trying to take eyewitness accounts,” he said. “With 50,000 potential eyewitnesses, by the time they get through with all of that, they’re left with a huge, confused mass.”

Houston police and fire officials said their investigation will include reviewing video taken by concert promoter Live Nation, as well as dozens of clips from people at the show. Officials also planned to review the event’s security plan and determine whether its organizers properly followed permit requirements.

Steven Adelman, vice president of the industry group Event Safety Alliance, said in an email that he sees no issue with public safety authorities authorizing an independent investigation of the Houston tragedy.

“I would hope and assume the investigation will be conducted by an outside person who is not subject to influence by the agencies that were involved with Astroworld. This is not an uncommon scenario in complex situations like this one,” wrote Adelman, whose organization was formed after the collapse of a stage killed seven people at the Indiana State Fair in 2011.

Adelman said private forensic analysis experts independently investigated the Indiana stage collapse, examining the stage roof engineering and crowd management.

“A good example of what I hope we see here,” Adelman said of the investigation in Houston.

Finner has defended how long it took for the concert to be called off after the first signs of trouble. The police chief said his department immediately notified concert organizers after noticing that attendees were “going down.” The event was called off 40 minutes later after discussions that included the fire department and park officials.

“You cannot just close when you’ve got 50,000 — over 50,000 — individuals, OK?” Finner said. “We have to worry about rioting — riots — when you have a group that’s that young.”

Peña said city officials limited the attendance to 50,000 even though the venue could have held 200,000 based on fire codes.

“It was the crowd control at the point of the stage that was the issue, especially as the crowd began to surge toward the stage,” Peña said.

Live Nation said in a statement that it is cooperating with local authorities “so that both the fans who attended and their families can get the answers they want and deserve, and we will address all legal matters at the appropriate time.”

County Judge Hidalgo tweeted on Saturday that she was “calling for an objective and independent investigation into what happened.” She also said her office was grateful for the work done by the police and fire departments.

“It may well be that this tragedy is the result of unpredictable events, of circumstances coming together that couldn’t possibly have been avoided,” Hidalgo said. “But until we determine that, I will ask the tough questions.”

Hidalgo’s office isn’t a law-enforcement agency and doesn’t have authority over criminal investigations.

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Kunzelman reported from College Park, Maryland. Associated Press reporters Kimberlee Kruesi in Nashville and Jake Bleiberg in Dallas contributed to this report.