A convicted felon accused of carrying out a string of deadly nighttime shootings in metro Phoenix late last year has been formally charged with murder in eight of the killings.

The charges come nearly two months after investigators said 35-year-old Cleophus Emmanuel Cooksey Jr. fatally shot nine people between late November and mid-December in Phoenix, Glendale and Avondale.

The victims include Cooksey's mother and stepfather and a 21-year-old man killed while selling marijuana to Cooksey, police said. It's unclear why the indictment — filed Thursday and made available publicly Monday — charges him in only eight of the nine killings.

Investigators say Cooksey is linked to the killings through ballistics and other evidence, such as a necklace belonging to a victim that Cooksey was wearing at the time of his Dec. 17 arrest.

A handgun stolen from one victim and a blue bandanna used to hide the suspect's face after another killing were found at his mother's apartment in the aftermath of her shooting death, investigators said. And a cellphone belonging to Cooksey and a shirt containing his DNA were found in a vehicle owned by a 43-year-old woman whose partially nude body was discovered in an alley after she was sexually assaulted, police said.

Cooksey, described by authorities as an aspiring musician, previously pleaded not guilty to charges stemming from the deaths of his mother and stepfather. Gary Beren, one of his court-appointed attorneys, didn't immediately respond to a phone message and email late Monday afternoon seeking comment on the indictment.

Investigators say Cooksey knew some of the victims. Police are still trying to determine the motive.

Four months before the killings started, he was released from prison on a manslaughter conviction for his participation in a 2001 robbery of a strip club where an accomplice was fatally shot.

He grew up in a household plagued by domestic violence, left home at age 16 to live with his girlfriend and started serving his manslaughter sentence at 19.

Cooksey, who has been denied bail, has an arraignment hearing scheduled for Friday.

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