Mills was evaluated by medical staff at the jail and was transported to Northside Hospital by ambulance for injuries.
Detectives say that during the course of the investigation, they obtained jail surveillance video that showed Allen strike Mills and Mills fall to the ground.
On July 6, detectives charged Allen with one count of Aggravated Battery.
On July 10, Mills was transferred from Northside Hospital to Bayfront Health St. Petersburg Hospital.
Detectives say that Mills' medical condition worsened while he was at Bayfront Health St. Petersburg Hospital and he died on Tuesday.
The Medical Examiner's Office will conduct an autopsy to determine cause and manner of death.
Allen was originally arrested by the Clearwater Police Department in December of 2017 and booked into the Pinellas County Jail for Possession of Powder Cocaine, Sale and Delivery of Powder Cocaine, Violation of Probation for Sale and Delivery of Cocaine, 1st Degree Murder, and 1st Degree Murder (Mother Unborn Child).
Mills was originally arrested by the Pinellas County Sheriff's Office in June of 2018 and booked into the Pinellas County Jail for Failure to Register as a Sex Offender, Failure to Obtain/Update Sex Offender ID, and two Hillsborough County warrants for Failure to Register as Sex Offender and Failure to Report Name or Residence.
Additional criminal charges are possible pending the outcome of the investigation. The investigation continues.