A California serial killer who authorities say strangled and raped at least seven women was fatally choked himself in a state prison, officials said Wednesday. Roger Reece Kibbe, 81, known as the “I-5 Strangler” in the 1970s and 1980s, was spotted unresponsive Sunday in his cell at Mule Creek State Prison southeast of Sacramento — his 40-year-old cellmate standing nearby. An autopsy showed Kibbe had been manually strangled, the Amador County Sheriff’s Office said, calling the death a homicide.