Shelly Shears and her boyfriend, Billy Stephens, got into an argument, police said. At some point, she allegedly struck him with her vehicle, and he died at the hospital from his injuries. (Mugshot: Case Grande Police Department)

Police in Case Grande, Arizona, claim a woman fatally struck her boyfriend with her vehicle after they got into an argument. Shelly Shears, 51, was booked into the Pinal County Adult Detention Center for second-degree murder.

Officers said they responded on Saturday at approximately 8:38 a.m. to a car-on-person collision in the 600 block of West Saguaro Street. They found Billy Stephens, 59, badly wounded, they said.

"Upon arrival, Officers discovered the victim, Billy Stephens, lying near the roadway suffering from what appeared to be significant trauma," police wrote. "The suspect, Shelly Shears, was on scene near the victim. Mr. Stephens was flown to a Phoenix-area hospital where he succumbed to his injuries. Casa Grande Police Department Detectives and the Critical Accident Investigation Team took over the investigation."

Detectives claimed to find evidence that Shears and Stephens were arguing before she struck him with her vehicle. Officers did not immediately detail the reason behind the argument and did not suggest a motive. Police did not immediately respond to a Law&Crime request for more information.

Shears is held without bond and scheduled for a court hearing on May 30. Officers said they forwarded the case to the Pinal County Attorney's Office for review.

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