Police say the investigation started when a Phoenix officer noticed something suspicious while first responding to a call about Cooksey and took the right steps.
Phoenix police Chief Jeri Williams said ballistic evidence collected from each homicide scene tied Cooksey to all homicides.
Court records show Cooksey had a previous criminal record for armed robbery and manslaughter 16 years ago. He was released from prison about a year ago and was in and out of jail since.
On Thursday, detectives added seven additional counts of homicide, seven counts of prohibited possessor of a firearm, one count of sexually motivated kidnapping, one count of firearm theft, and one count of armed robbery with a deadly weapon.
If you have any information about any of these crimes call Avondale police, Glendale police or Phoenix police. You can also call Silent Witness at 480-WITNESS.