The crowd at a music festival planned by Travis Scott, a favorite local rapper turned megastar, was expected to be difficult to control, according to concert organizers and Houston city officials. That’s what happened the last time Mr. Scott held his Astroworld Festival two years ago.

They braced themselves for months, adding dozens more officers from the Houston Police Department and more private security hired by the concert organizer, Live Nation.

The Houston police chief, who knows Mr. Scott personally and believes the musician has been doing good for his hometown, said he visited Mr. Scott in his trailer before his show on Friday and expressed concerns about the crowd’s energy, according to a person with knowledge of the chief’s account.

Fans had been drawn to see Mr. Scott because of the atmosphere, as well as the excitement of seeing music live again after the pandemic hiatus, for months. They arrived by plane from California and Colorado, and by car from Dallas and San Antonio. Ticket prices ranged from hundreds to thousands of dollars. Among the 50,000 spectators were elementary school students.

But the excitement turned to dread almost as soon as Mr. Scott took the stage at 9 p.m. on Friday, as the crowd erupted uncontrollably, confirming officials’ and concert organizers’ worst fears. Two 14-year-olds and a 16-year-old were among the eight people killed in the crush and chaos.

By Sunday, the Houston Police and Fire Departments had taken over the investigation into what happened at the NRG Park festival. Officials said they had compiled a rough timeline of events, attempting to piece together the movements of the swollen crowd as well as the actions of the private security and medical personnel on hand, as well as city police officers and emergency medical personnel.

The show ended 30 minutes earlier than planned on Friday night, but nearly 40 minutes after city officials declared a “mass casualty event.” One question raised by the tragedy was whether the officials could have stopped the show sooner; they claimed that doing so would have had its own risks, such as inciting a riot.

According to the 56-page planning report, event organizers planned to deploy security personnel throughout the arena, including along nearby roads, gates, fence lines, and VIP areas. They also erected imposing perimeters, including eight-foot scrim fencing, bike racks, snow fencing, and concrete bollards to maintain crowd control. According to officials, the fences and barricades were stronger and more robust than in 2019.

Mr. Anjum said the first wave of people seeking medical attention arrived around 3:30 p.m. However, nothing seemed out of the ordinary for a concert with a young audience, where overdoses are not uncommon.

By 8:15 p.m., the medical staff on hand reported that they were unable to document patients due to the large number of people in need. “Many patients were last seen conscious more than 20 minutes before receiving medical attention,” Mr. Anjum explained. They started triaging.

Paramedics were unable to keep up with the demand for naloxone, a drug that reverses the effects of an opioid overdose. Among them was at least one security guard who passed out after reporting that someone had stabbed him in the neck with a needle while he was attempting to help another person who had fainted.

Mr. Scott’s arrival was being counted down by a clock. According to Chief Pea, crowds surged to the main stage, pressing in from the sides rather than from the front.

Even so, for many in the audience, the show was just a show, full of excitement and anticipation.

Around 9:30 p.m., the music came to a halt as an ambulance entered the crowd. Mr. Anjum received his first call for cardiac arrest around this time. It took 10 minutes to get through the crowd to the patient, he said.

By 10 p.m., people were trampling over each other inside the show, an act that made Afnan Hasan, 18, recoil in rage. “We were doing everything we could to help them,” he explained. “Others weren’t stepping up.”

The show concluded around 10:15 p.m. According to officials, the venue was cleared out without incident. The exits were sufficiently wide. Within an hour, everyone had left.