SAN DIEGO -- The assistance of a sharp-eyed citizen led to the prompt arrest of a man who allegedly robbed a Kearny Mesa bank, authorities said Wednesday.

The witness grew suspicious because 37-year-old Luis Bernardo Padilla of San Diego, entered the Union Bank branch office in the 7700 block of Clairemont Mesa Boulevard about 2:30 p.m. Tuesday after parking behind a nearby business, even though there were spaces in the bank's lot, the FBI reported.

Believing a holdup might be imminent, the citizen used a cell-phone camera to capture images of Padilla's vehicle and license plate, according to the FBI. At about the same time, a man inside the bank handed a demand note to a teller, and then fled with an undisclosed amount of cash.

Minutes later, the sound of a police helicopter crew flying over the area, using a loudspeaker to announce a description of the thief, prompted the witness to report what he'd seen.

About 3 p.m., an officer spotted Padilla driving the suspect vehicle in the area of Clairemont Drive and Denver Street, pulled him over and took him into custody.