TEMPE, Ariz. -- A Lyft rider in suburban Phoenix stabbed his pregnant driver, killing the woman and her unborn child before stealing her vehicle and driving nearly 150 miles before being arrested near the California line, authorities said Monday.Tempe police said Kristina Howato, 39, was in her third trimester of pregnancy and is survived by two other young children.They say Fabian Durazo, 20, was being held at a La Paz County jail on suspicion of two counts of first-degree murder and one count each of kidnapping and armed robbery, authorities said.It was unclear Monday if Durazo has a lawyer yet who could speak on his behalf.Howato was working early Sunday as a Lyft driver when she received a pickup request in west Tempe, said Sgt. Ron Elcock, a police spokesman.Durazo allegedly attacked Howato when they arrived at an apartment complex about a half-mile away and he fled in her SUV.Police officers responded to the apartment complex about 1:30 a.m. after receiving reports of a woman screaming in the parking lot.A witness, who did not want to show his face on camera, was the first person to render aid."She walked over to my neighbor's apartment there, that's where she was banging on the door, yelling for help," he told KNXV He said blood was coming from everywhere."I asked her what happened. She said she was stabbed. I tried to locate the wounds. I asked her where she was stabbed. She said, 'All over,'" the witness said.He said the woman vaguely described her attacker before going unconscious."Myself and my roommate's friend tried to do what we could do, as much first aid as we could, stop bleeding," he said.Officers found Howato suffering from multiple stab wounds. She was transported to a hospital where both she and the unborn baby died.Arizona Department of Public Safety officials used GPS tracking to locate the stolen SUV on Interstate 10 near Quartzsite, about 25 miles (40 kilometers) from the Arizona-California line and Durazo was taken into custody Sunday afternoon.Police said they don't believe Durazo and Howato knew each other and a motive for the fatal stabbing remains undetermined."Throughout our careers as officers, we have incidents that really, really touch our hearts and stay with you throughout your careers," Elcock said at a news conference. "This is definitely one of those incidents that really is going to affect the police department for a long time."A statement from officials with San Francisco-based Lyft said: "We were shocked and deeply saddened to learn of this tragedy, and our thoughts are with the family and friends of the victims."Lyft says it is assisting with the investigation, adding that the passenger's account has been permanently deactivated.