Tennessee State Democratic Caucus Senator Jeff Yarbro talks with editors and reporters Thursday, August 13, 2015 at the Chattanooga Times Free Press.

NASHVILLE -- A West Tennessee inmate died from natural causes, according to prison officials, but an autopsy showed he died from multiple traumatic injuries — and a state senator said Monday that Gov. Bill Haslam should further investigate the case.

The Tennessean newspaper in Nashville reported about the death of 55-year-old Elbert Thornton in its Saturday edition.

State prison records obtained by the newspaper say Thornton died of natural causes at the West Tennessee State Penitentiary in 2013. But the doctor who pronounced Thornton dead at an area hospital reported numerous bruises on Thornton's head and what "appeared to be whip marks" on his upper abdomen.

An autopsy conducted by a doctor at the West Tennessee Regional Forensic Center in Memphis listed Thornton's cause of death as "multiple blunt traumatic and thermal injuries," the newspaper reported.

"Autopsy show multiple blunt traumatic injuries to the head and neck, torso, and extremities," the autopsy summary states. He had burns on his genitals and thighs.

Democratic Sen. Jeff Yarbro of Nashville told reporters on Monday that a natural death isn't typically accompanied by such injuries.

"We need answers and we need them now," Yarbro said.

When asked about Yarbro's call for an investigation, Haslam spokesman Dave Smith said in an email that "a full investigation was completed, and the death was reviewed by the Mortality and Morbidity panel."

"The case was presented to the local District Attorney's Office for review, and it's my understanding charges were not pursued," Smith said.

Correction Department spokeswoman Neysa Taylor also stated in an email that "Thornton had multiple medical complications that contributed to the autopsy findings.

"While any in-custody death is unfortunate, they do happen from time to time due to our aging offender population and the variety of ailments that inmates have when they enter our custody," she said.

Questions about Thornton's death come amid staffing and security problems that have led to multiple legislative hearings and a controversial on-site review of several Tennessee prisons.

However, state prison officials continue to downplay reports of an increase in violence within the walls of Tennessee's prisons.