Autopsies have been completed on three undocumented immigrants who were fatally shot last week in the desert northwest of Tucson.
Each of the victims died from a single gunshot wound, said Lt. Michael O'Connor of the Pima County Sheriff's Office.
Some of the victims were carrying identification but investigators are not sure if it was real so they are processing fingerprints through a national database to determine their identities, O'Connor said.
County authorities found a vehicle with blood in it Tuesday that may be linked to the Feb. 8 shooting incident that killed three people and wounded two others.
On Monday, a daylong ground and air search failed to turn up new evidence tied to the shootings, said Rick Kastigar, criminal investigations chief for the Pima County Sheriff's Department.
Some 20 to 25 deputies and investigators searched the area around the Silver Bell mine in an airplane, on horses and on all-terrain vehicles without success.
But on Tuesday, investigators were following up on a vehicle found near the Pinal Air Park with blood in it. "We're guessing it may be the secondary vehicle that transported the wounded," he said.
"We know it was stolen out of Phoenix and has blood in it," Kastigar said. "Whether it was related to this event has not been determined."
On Feb. 8, gunmen in a vehicle tried to force a pickup truck carrying about 20 immigrants to stop along a dirt road in the Ironwood Forest National Monument.
After several miles, the pickup ran off the road.
The three injured people, including one man mortally wounded, were given a ride in a second vehicle. It was driven by either a prearranged secondary smuggler or a good Samaritan for several more miles. Then the people were ordered out — possibly when the driver saw a large amount of blood, authorities said.
Investigators were trying to determine whether the vehicle found was the one that carried those wounded.
Authorities said evidence gathered so far in the case still points to smugglers but a motive for the shootings remains unclear.