ALLENTOWN, Pa. (AP) - A car explosion that rocked downtown Allentown left three males dead, including the likely "perpetrator," officials said Sunday as federal authorities who are leading the investigation looked ahead to autopsies.

"We know there's been a criminal incident," District Attorney James Martin told reporters at a news conference Sunday. "We have a high degree of confidence that the perpetrator was probably killed in the incident."

Authorities released no information about the possible cause of Saturday night's blast, including whether it was a bomb, but Martin said, "Loads of us in law enforcement" are confident "this was A. an isolated incident and B. there's no continuing threat."

Authorities are seeking the public's help in getting clues and asked anyone with information to call the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, which is leading the investigation.

The blast occurred a block from the PPL Center sports arena and two blocks from the popular Hamilton Street dining area in Allentown, a city of about 120,000 about 60 miles (95 kilometers) northwest of Philadelphia. The block where it occurred is a mixture of residences and small businesses, including a restaurant and a bar.

The FBI, state police, and city and county authorities are investigating along with the ATF.

Resident Carlos Perodin told The Morning Call of Allentown that he was watching a movie with his wife when he heard a thunderous explosion and went to the scene.

"The fire was crazy," he said. "The car was pretty much split in half."

Another witness to the aftermath of the explosion, Stephanie Connelly, told The Morning Call that she saw body parts strewn across the street.

"This is real life and I'm shaking and freaking out while I'm running," she said.

Autopsies were planned Monday on the three males found dead after the 9:30 p.m. explosion, Lehigh County Coroner Scott Grim said Sunday afternoon. Grim said he would probably be able to release the names Monday once their identities are confirmed and their families are notified.

Authorities swarmed the area after the explosion. A bus station was turned into a makeshift command center with armored vehicles, dozens of police cruisers, mobile command units and even portable bathrooms, the paper reported. Several portable tents were also erected for evidence processing.

Residents were asked to avoid the area, and people who live nearby were asked to shelter in place. A shelter was set up at an elementary school.

The FBI had earlier said it was working with other agencies and "to assess the situation and determine the cause, with public safety the bureau's highest priority." Officials asked anyone who witnessed the blast or had information about it to contact investigators.