(CNN) -- Five teenagers who died of apparent carbon monoxide poisoning in a Hialeah, Florida, motel room had gathered to celebrate a birthday, police said Tuesday.

Although an official cause of death won't be released until autopsies are completed, the investigation so far shows the teenagers apparently died because they left a car with a troublesome starter running in a closed garage beneath their room, police spokesman Carl Zogby said.

"Unfortunately, whoever could tell us what the intent of leaving the car on (was) is dead," Zogby said. "But we are being told by some friends that it probably had starter engine trouble."

"All the evidence indicates clearly a carbon monoxide poisoning," he said, noting no alcohol or drugs were found in the room the five had rented at the Hotel Presidente.

Zogby identified the dead as Juchen C. Marctial, 19; Peterson Nazon, 17; Jonas Antenor, 17; Jean Pierre Ferdinand, 16; and Evans Charles, 19. All were from the same neighborhood north of Miami, according to police.

They had gathered Sunday night to celebrate Marctial's 19th birthday that day, according to police.

A maid at the hotel discovered the bodies and called 911 Monday afternoon, Zogby said.

Fire crews tested the air in the room and found a high concentration of deadly carbon monoxide, a primary ingredient in car exhaust, in the room where the bodies were found, Hialeah Fire Department Lt. Cesar Espinosa said.

The room is located upstairs from a private garage for the room's occupants. The door between the garage and the room was open when crews arrived, Espinosa said.

It's unclear whether the room or garage had working carbon monoxide detectors, or whether it was required to have such devices. Zogby said city investigators are looking into that issue.

Autopsies began Monday night and were expected to continue Tuesday. Zogby said he was uncertain when results from toxicology tests that would confirm investigators' suspicions would be available.

CNN's Samuel Garder contributed to this report.