"Mr. Treadwell had a gunshot wound to his upper torso," Sgt. Maggie Cox, of the Phoenix Police Department, told ABC News affiliate KNXV-TV. "The gunshot came from outside the vehicle. We don't know much more than he suffered a gunshot wound and died."
On Tuesday, Treadwell's wife, Frances Treadwell, told ABC News that she'd spoken to him at around 12:28 a.m. on Sunday morning. They wished each other a happy anniversary and told each other "I love you," she said. The first 911 call reporting the shooting came around 12:35 a.m., she said. He'd been shot through the car window.
She said the final phone call was a "gift from God."
"I truly believe [God] enabled me to talk to him one more time," she said. "I'll forever, forever cherish that phone call."
Frances Treadwell described her husband as very popular in school and an athlete. She said he was a father, grandfather and even great-grandfather who had four brothers in Indiana.
"Everybody loved him. ... He was my better half. My true soulmate, for sure," she said. "He was just my best friend. So losing him has been very traumatic but he left behind lots of good things, lots of good memories, lots of good times with family and friends. ... We had a good life."
Frances Treadwell told ABC News that her husband was retired but enjoyed driving, particularly at night, and loved meeting people. She said any extra money that he made from the job was used on trips for the two.
The night he was shot, she said he'd commented during the call with her that he was in a neighborhood that he didn't feel safe in and the two got off the phone.
She said when she tried calling him at 4 a.m., he didn't answer. About 5 a.m., she said her son woke her up with the horrible news.
Frances Treadwell said she was speaking out publicly to encourage anyone with any information about the shooting to come forward and speak to the police.
"I'm really hoping he didn't suffer. ... You would have loved Harry," she said. "He just looked like Santa Claus. He just was so gracious. You just don't find many people like him in the world. ... This is a senseless act of violence."
Police said there were no suspects and they were hoping that anyone with any information would contact them.
"Right now, we're not having any indication that he was maybe a target. ... We're really heavily depending on the community's assistance. ... This is one of those crimes, it just touches everybody. You know, ride-sharing, we all use it so it's a very sensitive topic," Cox told ABC News on Tuesday. "It's a high priority for us."
In a statement, Lyft spokeswoman Lauren Alexander said the company was "deeply saddened and shocked" by Harold Treadwell's slaying. Alexander said the company had reached out to the Treadwell family and that at the time of the shooting, no rider was in the car with Harold Treadwell and he had not accepted another ride for pickup.
"Our sympathies go out to the loved ones of Harold Treadwell and all those impacted by this tragedy. We are actively assisting law enforcement and will continue helping in any way we can," she said.
ABC News' Clayton Sandell and Becky Perlow contributed to the reporting in this story.