PRESCOTT, Ariz. (AP) — The 19 firefighters killed over the weekend in an Arizona blaze died of burns and inhalation problems, according to initial autopsy findings released Thursday.

Cari Gerchick, a spokeswoman for the Maricopa County Medical Examiner's Office in Phoenix, said the Hotshots died from burns, carbon monoxide poisoning or oxygen deprivation, or a combination of the factors. The autopsies were performed Tuesday, but more detailed autopsy reports should be released in three months, pending lab work.

"Our work is not done," Gerchick told The Associated Press. "But what we are glad about is that we can release these fallen heroes to their families for burial, and that grieving process can continue."

The Prescott-based Hotshots' bodies will be taken back to the hilltop community in a 75-mile procession from Phoenix on Sunday. Each firefighter will be in an individual hearse, accompanied by motorcycle escorts, honor guard members and American flags.

A memorial service planned for Tuesday is expected to draw thousands of mourners, including the families of the firefighters.

The firefighters had deployed Sunday to what was thought to be a manageable lightning-caused forest fire near the small town of Yarnell, about 60 miles northwest of Phoenix.

Violent winds turned the fire and trapped the highly trained Hotshots, most of them in the prime of their lives. Fire officials said the crew had deployed their fire shelters, which can briefly protect people from blazes.

It was the nation's biggest loss of firefighters since 9/11.

Sunday's tragedy raised questions of whether the Hotshot crew should have been pulled out much earlier and whether usual precautions would have made any difference in the face of triple-digit temperatures, erratic winds and dry conditions that caused the fire to explode.

A team of forest managers and safety experts is investigating what went wrong and plan to release some initial findings by the weekend. In addition to examining radio logs, the fire site and weather reports, they'll also talk to the crew's sole survivor, a 21-year-old lookout who warned his fellow firefighters and friends that the wildfire was switching directions.

Nearly 600 firefighters continue to fight the blaze, which was 45 percent contained Thursday morning. The fire has destroyed more than 100 homes and burned about 13 square miles. Yarnell remained evacuated Thursday, but authorities hope to allow residents back in by Saturday.

Already, residents of Peeples Valley were going to be allowed back into their homes Thursday night, said Yavapai County Sheriff Scott Mascher.

Meanwhile on Thursday, Prescott officials were working to retool the city's traditional over-the-top Independence Day celebration in the wake of the tragedy.

They plan to still shoot off fireworks despite tinder-dry conditions as the community of 40,000 tries to mourn its dead without compromising its history. The mantra for days has been, "celebration, not grief."

Fire officials say they will be able to deploy the pyrotechnics safely, pouring water on the detonation area if necessary.