A US serial killer linked to the murders of six men and wounding of a woman is "on a mission", police have said.
Ballistics and video evidence have linked the crimes which date back to last year, in the central Californian cities of Stockton and Oakland. The cities are about 110 kilometres apart.
"We don't know what the motive is. What we do believe is that it's mission-oriented," Stockton Police Chief Stanley McFadden said.