(CNN) -- Authorities in the southern Mexican state of Michoacán said Thursday that no suspects have been arrested in connection with the brutal murder last week of a U.S. teen and two of his Mexican friends.
The charred bodies of 18-year-old Alexis Marron, from suburban Chicago, Juan Pedro Estrada Ocegueda, 24, and Raul Vazquez, 19, were found in the trunk of a car burned to its shell in a remote rural road, according to the Michoacán state attorney's office.
An investigator with the state attorney's office, who declined to give her name for fear of retaliation, said the sister of one of the victims identified her brother's body and the car. Authorities made the gruesome discovery at 7 a.m. on Christmas Eve day, after relatives had reported the men missing the night before, the investigator said.
The investigator said that Marron, who was visiting his grandmother and other relatives in the town of Quiringuicharo for the holidays, asked Estrada Ocegueda to give him a ride to a nearby town so he could visit his girlfriend.
"Vazquez was just riding with them when they went missing," the investigator said.
The bodies were found in Ixtlan de los Hervores, a town known for its thermal springs, about 80 miles southeast of Guadalajara.
Violence in Michoacán has increased sharply in the last few years amid a bloody turf war between two ruthless drug cartels.
In Rolling Meadows, Illinois, close friends of Marron say they can't understand why anyone would want to kill the high school senior.
Brandon Leo told CNN affiliate WBBM in Chicago that his friend was not the type of person who went out looking for trouble.
"I want people to know that he was a good kid," Leo said of Marron. "He was honest with everyone. He always had that smile. He was warm-hearted. He was just a great kid. This shouldn't have happened."
Kyle Gentile said he's trying to cope with the loss. "No one ever would deserve this, but the way that he went is just so horrible that I couldn't even believe it when someone told me," Gentile said. "I thought it was a joke."
Daniela Zendejas, 17, a cousin of Marron's who also attends Rolling Meadows High School, said Marron was "always smiling, happy. He enjoyed life."
"He wanted to see my grandma and my aunts and uncles over there," Zendejas said. "We used to travel there together, but this time he was alone."
Estrada Ocegueda had described himself, on his Facebook page, as somebody who loves having fun with friends. "I'm a happy young man, but I don't drink," he wrote.
This is not the first time charred bodies have appeared in Michoacán.
La Voz de Michoacán, a local newspaper in Morelia, the capital, reported on December 17 that two bodies were found inside a truck that also was gutted by fire. According to the newspaper, the victims were traveling on the highway that connects Mexico City to Guadalajara.
No suspects have been arrested in that case.