The FBI has added $25,000 to a reward set up to catch the killer of a teenager who was set on fire last month in a case that rocked a small Mississippi town and drew national attention, authorities confirmed to FoxNews.com.

The federal funds bring to $43,000 the total amount being offered for information leading to the person who killed 19-year-old Jessica Chambers, who was found alive, but badly burned and staggering along the side of a Panola County road on Dec. 6. Investigators remain baffled, but Panola County District Attorney John Champion said he hopes the money might yield more clues in the murder.

"I still have hope that people will do the right thing regardless of monetary benefit, but we can't ignore the fact that money can be a driving force."

- District Attorney John Champion

"I still have hope that people will do the right thing regardless of monetary benefit, but we can't ignore the fact that money can be a driving force," Champion told FoxNews.com Tuesday. "This is the most frustrating case I’ve ever had to deal with in my 22 years in law enforcement."

Chambers, of Panola County, was found shortly after 8 p.m. on Dec. 6 with burns covering more than 98 percent of her body. When emergency responders arrived at the scene, Chambers was walking away from her burning vehicle and able to utter a few words to them about the attack -- though authorities have not said what, if anything, the young woman was able to communicate.

Panola County Sheriff Dennis Darby said last month Chambers was doused with a flammable liquid before she was set on fire on a road in Courtland, Miss., a town with a population of 460 people.

Authorities were quick to label her death a homicide, but have yet to identify a prime suspect in the case, despite interviews with more than 100 people, Champion told FoxNews.com. 

Investigators examined surveillance video of Chambers visiting a nearby gas station the night she was killed. The footage shows Chambers walking toward the gas station before being called away by someone out of the camera's view. The video was recorded about 90 minutes before Chambers was found burned alive on a road less than a mile away from the gas station. 

In an interview with FoxNews.com, Ali Alsanai, the gas station's owner, said he saw Chambers when she visited the gas station that night and the two exchanged a few words.

"Just small talk," Alsanai said of the conversation. "I wasn’t really paying attention because I was busy that day." Champion said Alsanai was cleared as a suspect. 

Over the past month, authorities have also been pored over the teen's cellphone records for clues in the case. Chambers' phone was found by investigators at the scene.

"She was the most beautiful and loving and kind girl I've ever known," Chambers' best friend, Alyssa Cotten, told FoxNews.com last month.

"She loved to cheer. She loved softball. She loved her family and her friends. She was just a big bundle of joy," said Cotton. "We have no idea who did this."

The teen's father, Ben Chambers, who works as a mechanic for the Panola County Sheriff's Department, said he hopes his daughter's last words will lead to her killer. 

Anyone with information on the murder is urged to contact the Panola County Sheriff's Office at 662-563-6230.