A man traveling east on West Irvington, west of South Mission roads went off the road and crashed into a tree Wednesday morning.
A Pima County Sheriff's Department detective who was in the area working a case witnessed the crash and went to help the man, said Deputy Jesus Bañuelos, a department spokesman.
The man, who was driving a Hummer, told the detective he was shot. The detective, who rendered aid, called for paramedics who treated the man and took him to University of Arizona Medical Center with life-threatening injuries, said Bañuelos.
Shortly after 11 a.m., deputies were responding to a 911 call reporting shots fired in the area when the detective informed deputies of what he encountered at West Irvington and South Cactus Wren, Bañuelos said.
Deputies were investigating leads in the shooting.