(CNN) A dozen prisoners have died in the custody of Mississippi authorities this month and, with the exception of two deaths that remain under investigation, there's no indication as to what killed them.
The Mississippi Department of Corrections says investigations are underway in each of the deaths.
While DOC Commissioner Pelicia Hall said the number of deaths "is not out of line with ... previous months," the latest DOC figures showed 47 inmates died in 2015, 53 died in 2014 and 71 in 2013.
An after-hours email requesting a monthly breakdown of the numbers was not immediately returned.
Hall said in a Tuesday statement that the state's inmate population -- 19,425 as of Tuesday -- was composed of "people from all walks of life and with all types of pre-existing conditions."
"The department believes that a majority of the deaths are from natural causes in that they include cancer, coronary, and other medical conditions," her statement said.
Reports from CNN affiliates suggest that at least one inmate did not die from natural causes.
The day before Hall's statement, officers responding to a fight between two inmates found Nija Bonhomme, 24, of Pearl River, on the floor at the Wilkinson County Correctional Facility in Woodville, WLBT and the DOC reported.
On August 11, Ricky Martin, 58, died after telling fellow inmates he was having trouble breathing, according to CNN affiliate WTVA, which cited three inmates who were with Martin as he was dying and who spoke to the The Clarion-Ledger newspaper.
The inmates further told the paper that Martin sought help from corrections officials but was told to get away from the guard tower, the station reported.
The string of deaths began August 2 when 57-year-old murder convict Albert McGee died at South Mississippi Correctional Institution in Leakesville, according to the DOC.
Two more prisoners died August 4 and another two inmates died August 5. The latest death came Monday when Troy Pittman, 59, was pronounced dead at a hospital after being transferred from Central Mississippi Correctional Facility in Pearl, the DOC reported.
The oldest prisoner to die was a 70-year-old, the DOC said. There was one woman among the deceased inmates: Nicole Rathman, 33, who was pronounced dead at a hospital last week after being transported from Central Mississippi Correctional Facility.
According to The Clarion-Ledger and DOC, five prisoners have died at that prison this month, three died at the Mississippi State Penitentiary at Parchman, three died at South Mississippi Correctional Institution and Bonhomme, the youngest of the 12 inmates, died at Wilkinson County Correctional Facility.
The Bureau of Justice Statistics report states that Mississippi and Oklahoma had the sixth-highest inmate mortality rate in the nation, with 324 deaths per 100,000 state and federal prisoners between 2001 and 2014. Louisiana led the nation with 477, the report said.