William Donald Leonard II, 49, is suspected of stabbing an acquaintance soon after 7 p.m. on Saturday, March 1 at a motel in the 600 block of North Ramona Boulevard, Riverside County Sheriff's Department officials said.
Vanessa Christine Rodoracio, 28, is suspected of being related to the crime and may be traveling with Leonard.
The victim, who has not been unidentified, was taken to the hospital with a life-threatening stab wound and listed in critical condition.
Leonard is described as a white male adult, approximately 5 feet 10 inches tall and 200 pounds, with brown hair and hazel eyes. He was last seen driving a silver, 1999 Mercedes-Benz with a license plate 6ZQB633, authorities said.
Anyone with information about the incident or the whereabouts of the suspects is asked to contact the San Jacinto Police Department at (951) 654-2702 or Riverside County Sheriff's Dispatch at (951) 776-1099.