Cleophus Cooksey Jr.

PHOENIX — Phoenix-area police have evidence linking a 35-year-old man already charged with killing his mother and stepfather to seven additional homicides that occurred in a three-week span late last year, officials said Thursday.

Cleophus Cooksey Jr. knew some of the victims but investigators are still trying to determine motives for at least some of the killings, according to police officials in Phoenix, Glendale and Avondale.

A number of details were withheld by police who cited the ongoing investigation.

Cooksey was arrested Dec. 17 for the shooting deaths of his mother, Rene Cooksey, and stepfather, Edward Nunn, and he's jailed on two counts of first-degree murder and one of being a felon in possession of a gun.

Cooksey was rebooked into jail Thursday in the seven additional homicide cases, said Sgt. Jonathan Howard, Phoenix Police Department spokesman.

Cooksey previously served time in prison for manslaughter and armed robbery.

Officials said investigators were able to use evidence from shell casings to connect at least some of the killings.

Howard said a combination of physical and forensic evidence and witness statements enabled investigators to link Cooksey to all the killings.

"I'm just proud as heck that he's off the street," said Glendale police Chief Rick St. John.

Phoenix Mayor Greg Stanton said new technology allows police to get results of ballistic checks within hours instead of weeks and to more easily find connections between cases.

"It means crimes get solved more quickly," Stanton said.

The FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives provided support for the local agencies' investigation, officials said.

The Arizona Republic said Cooksey is the grandson of longtime Tucson civil rights leader Roy L. Cooksey, who died in 2009.