2 Killed in Unrelated Shootings in Santa Ana : Slayings: A 35-year-old man was shot during an argument over a bicycle, and a 17-year-old boy was fired upon while riding in the back of a car.

A teen-ager and a 35-year-old man were shot to death within hours of each other Tuesday afternoon in unrelated attacks, bringing the number of slayings in the city this week to four.

The first of Tuesday’s shootings apparently occurred during an argument between two men over a 10-speed bicycle, said Santa Ana police Sgt. Dick Faust.

Sergio Victor Rangel, 35, was shot in the head and chest just before 1 p.m. in the 1600 block of South Standard Avenue. The gunman then ran through the back of a vacant business, jumped over a brick wall and disappeared into a large apartment complex. He remains at large, and police don’t know who he is.

“It is unknown why the victim and the shooter were arguing over the bicycle or who the legal owner might be,” Faust said.

Rangel, a resident of Tustin, died at the scene.

The second killing occurred two hours later when a 17-year-old riding in back of a Chevrolet El Camino was shot as he and two other teen-agers were traveling north on Flower Street near Dyer Road.

“A beige Toyota Corolla came up behind them and began to ram the rear of the car,” Faust said. “The victims continued north and were fired upon by an occupant in the Toyota.” The attackers quit the chase in the area of Main Street and Warner Avenue.

After stopping, the driver realized that his passenger had been shot, Faust said.

The teen-ager, whose name was not released, was taken to Western Medical Center-Santa Ana, where he died a short time later. He was a resident of Santa Ana.

Since Sunday, four people have been shot to death and another person seriously injured in a series of incidents that police say are unrelated.

On Sunday, three gunman chased and fatally shot 20-year-old Omar Cisneros on the sidewalk outside his home on South Baker Street. The assailants reportedly fired into Cisneros’ body even as he lay on the ground.

Earlier that day, the body of 28-year-old Fidel Cruz Robles of Santa Ana was found in an alley on South Standard Avenue with a gunshot wound to the head. The motive appears to be robbery, police said.

On Monday night, 21-year-old John Villalobos of Santa Ana was seriously wounded during a gun battle on a downtown street. Villalobos, who was in guarded condition Tuesday at Western Medical Center-Santa Ana, was driving near the intersection of 1st Street and Broadway when he became involved in an argument with a pedestrian and the two men pulled out guns.

So far, no arrests have been made in any of the shootings, Faust said.