Santa Clara County's new district attorney, Jeff Rosen, Wednesday announced the formation of a unit that will use DNA evidence to investigate unsolved crimes, fulfilling a promise he made at the outset of his campaign.

The cold-case unit will use DNA evidence to investigate unsolved murders, rapes and violent assaults.

Rosen signed a "Partnership and Cooperation Agreement" with Sheriff Laurie Smith and the chiefs of police. The agreement allows the District Attorney's Office to have greater access to unsolved cases in order to locate and submit biological evidence, interview witnesses, and conduct comprehensive case evaluations.

The county crime lab will handle DNA.

Rosen appointed veteran prosecutor Ted Kajani to head the unit. Kajani has focused on cases involving homicide, sexual assault, domestic violence and stalking. He has been with the district attorney's office since 1994 and previously served as California's deputy attorney general.

Nate Wandruff was named the unit's criminal investigator. Prior to coming to the district attorney's office in 2009, Wandruff spent 11 years working for the Mountain View Police Department.