LOS ANGELES, Jan. 18 (Xinhua) -- A suspected, who may have killed nine people in the Phoenix area in southwestern U.S. state of Arizona in three weeks in late 2017, was arrested by police, officials said Thursday.

At a press conference, Phoenix police Chief Jeri Williams said that they had evidence showing 35-year-old Cleophus Cooksey had killed seven more people between Nov. 27 to Dec. 17 in Arizona. Cooksey was arrested last December for alleged killing his mother and step-father.

Willianms said the new technology of ballistics testing had helped detectives to get results of ballistics checks and find out Cooksey had connection to other homicides.

However, investigators had not been able to establish a motive or connection between Cooksey and the victims, who were in a variety of demographic groups, Williams said.

Phoenix Police Sergeant Jonathan Howard also told reporters that there was "a distinct possibility" Cooksey may have killed others who have not yet identified.

Cooksey was reported previously served 16 years in prison for manslaughter and armed robbery.