(CNN) -- Mystery surrounds the fiery weekend death of Jessica Chambers, but the Mississippi teen may have given firefighters a clue in her killing, a prosecutor said Wednesday.
The volunteer fire department that responded to her car blaze Saturday night got there quickly because it was at another call a couple of miles away, said John Champion, district attorney for Mississippi's 17th Circuit.
When firefighters arrived, Chambers approached one of them and spoke. She was not on fire, as has been widely reported, the prosecutor said.
Champion didn't divulge what she said but told CNN, "It has certainly given us a lead we're following up on."
Though authorities are releasing sparse details of the crime and investigation, they have determined an accelerant was used in the blaze, but it's not clear whether the accelerant was poured on the car or Chambers herself, Champion said.
The state fire marshal is processing the evidence to determine what type of accelerant, and it's possible the evidence will need to be sent to the Bureau of Alcohol, Tobacco, Firearms and Explosives in Atlanta, he said.
Investigators believe her phone will be "the key to everything," the prosecutor said. She received a call before she left her house, he said.
Despite reports she was going to a party, her appearance -- her hair was in a bun and she was wearing camouflage pajama pants -- suggests that wasn't the case, Champion said. Police have also spoken to partygoers, who don't recall seeing her there, he said. The prosecutor also said investigators found no evidence in a store surveillance video that appears to show Chambers pre-paying for gas. She walks to the store's front door when something or someone catches her attention.
She waves and walks off camera briefly, comes back into the camera's view, enters the store where three men chat by the doorway and spends about a minute at the counter before going back outside and pumping gas.
The business, which Champion characterized as a rural mom-and-pop store, is about two miles from Chamber's home. She purchased something to drink there, the prosecutor said.
A Facebook page titled Justice for Jessica has drawn more than 63,000 likes and that number was climbing rapidly Wednesday afternoon. The page states it was created "to keep Jessica's name alive & out there."
Firefighters found Chambers and her car in a wooded area near Courtland, Mississippi. Her sister, Amanda, told CNN affiliate KTSM that Jessica had burns over 98% of her body when she died Sunday. An autopsy was performed but results have not been made public.
"Nobody deserves what she went through," her sister told the station from her home in Fort Bliss, Texas. "She was a cheerleader. She was really well-known. She was loved."
Amanda's husband was on his way home from overseas Tuesday, she told KTSM. When he arrives, they'll travel to Mississippi to be with Amanda's family.
"They have ripped everything I have," Jessica's mother, Lisa Chambers, told CNN affiliate WMC.
The teen had left the house to clean out her car and get something to eat before her death, her mother said.
CNN's Steve Almasy, Dave Alsup and John Murgatroyd contributed to this report