The Associated Press is reporting Maricopa County officials say a 60-year-old inmate in Sheriff Joe Arpaio’s tent city has died from cardiac arrest.

Authorities believe the inmate died of natural causes but an investigation has been launched into his death.

Reporter Aurelia Fierros at published the inmates name along with more details of the incident:

Officers found Arthur Madril unresponsive in his bunk, at the Maricopa County jail, on Saturday.

Madril was in custody on a $4,000 child support warrant and had been booked into custody in September. He was on work release status, being able to work during the week and report to jail on nights and weekends.

The prisoner had returned to jail Friday night and was found unresponsive by detention officers in the morning. CPR was performed but a Phoenix Fire crew, pronounced him deceased.

Sheriff Arpaio celebrated Tent City’s 19th anniversary in August 2012. CBS affiliate KPHO reports there have been at least two other deaths in Tent City:

In 2003, Brian Crenshaw died after what was determined to be a beating by jail guards. His family sued and was awarded $2 million.

That same year, Phillip Wilson was serving two months for a non-violent offense and was attacked, beaten and killed by white supremist gang members. A suit was also filed in that death, but MCSO was not held responsible.

In June 2012, more than 1,000 demonstrators gathered at a rally to call for the closure of the sheriff’s complex of canvas jail tents. Organizers claim conditions in Arpaio’s “Tent City” complex are inhumane. Complaints include dangerous temperatures in the tents that rise above 125 degrees during the Summer.