A serial killing suspect shot and killed nine people, including his own mother, and used a victim’s gun in some of the deaths that unfolded in a three-week span late last year, US authorities have said.

Shell casings, DNA, stolen jewellery and a mobile phone taken from a victim were among the pieces of evidence that investigators used to tie Cleophus Cooksey Jr, 35, to the killings, according to court documents.

“It should appall every one of us in the room that he managed to kill nine people period, let alone in such a short period of three weeks,” said Sergeant Jonathan Howard, a police spokesman in Phoenix, Arizona.

The seven men and two women were shot between November 27 and December  17 in their homes, suburban apartment complexes, in a parked car or while outside, the documents state.

Cooksey, described by police as an aspiring musician, knew some of the victims but investigators were still trying to determine motives in a few of the attacks, according to police officials in Phoenix, Glendale and Avondale.

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

The victims included Jesus Real, 25, the brother of Cooksey’s ex-girlfriend. Real was asleep in his Avondale home on December 11 when he was shot twice in the face. Avondale police say Mr Real’s sister and Cooksey had broken up the night before.

Another victim, 43-year-old Maria Villanueva, was seen on surveillance video arriving at a Glendale apartment complex on December 15 and then leaving with an unknown man in the driver’s seat.

Her partially nude body was found the next morning in a Phoenix alley and her car was found abandoned at another complex in Glendale.

Investigators found a mobile phone and a bloody men’s shirt inside. DNA on the shirt matched Cooksey’s, court documents said. The mobile phone was also confirmed to be his.

Cleophus Cooksey in an image released by police (AP)Cleophus Cooksey in an image released by police (AP)

Cooksey was arrested on December 17 for the shooting deaths of his mother and stepfather in their home and has been jailed since then on two counts of first-degree murder and one count of being a felon in possession of a weapon.

He was re-booked into jail on Thursday in the seven additional homicide cases, Sgt Howard said.

“I’m just proud as heck that he’s off the street,” said Glendale police chief Rick St John.

Cooksey previously served 16 years in prison for manslaughter and armed robbery and had been free for 18 months, authorities said.

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,” Mr Stanton said.

Cooksey was arrested on December 17 for the shooting deaths of his mother and a man and he is jailed on two counts of first-degree murder and one of being a felon in possession of a weapon.

Investigators were able to use evidence from shelling casings to connect at least some of the killings, officials said.