Jul 7, 2013 2 min read

SIMI VALLEY, Calif. (AP) – Fire crews have combed a community park northwest of Los Angeles in search of clues after a July Fourth fireworks explosion injured dozens of revelers.

The Ventura County Fire Department completed its evidence collection Saturday at a Simi Valley park where between 8,000 and 10,000 spectators gathered days earlier to watch fireworks. Crews also gathered evidence in nearby Ojai, where a pyrotechnics operator was injured by a premature blast.

“We’ve collected everything we need to collect” from the Simi Valley site 40 miles northwest of Los Angeles, Ventura County fire spokesman Mike Lindbery told the Ventura County Star.

A state fire official was due in town this week to join county fire officials on the investigation.

The community park remained closed after Thursday’s mishap. Some three dozen spectators, ranging from 17 months to 78 years old, were injured in the fireworks explosion. Fire and hospital officials said some had burns and shrapnel cuts while others were trampled on as the crowd rushed to safety.

Police initially said it appeared a firework detonated prematurely shortly after the show began, creating a cascading effect. But fire officials later said they needed more eyewitness accounts and details from the pyrotechnics company before determining a cause.

Crews spent the past several days at the park, collecting unexploded fireworks, photographing the site and transporting evidence to another location. Others studied the scorched grounds to determine how far debris flew.

Investigators also planned to review cellphone videos taken by revelers in the chaotic aftermath, Lindbery told The Associated Press.

In nearby Ojai, a fireworks show at a high school ended 15 minutes early after a pyrotechnics operator was struck by exploding fireworks.

The state Division of Occupational Safety and Health told the Star the unidentified man suffered serious injuries to his face, left arm and left leg.