San Jose police, with the help of a security guard, arrested a 70-year-old man this week on suspicion of kidnapping and molesting a 13-year-old girl that he was hired to drive home from school, according to the police department.

Tuan Binh Nguyen of San Jose was taken into custody Monday in a business parking lot after Christopher Gomez, a security guard with Valiant Private Security, witnessed and stopped an alleged sexual assault in progress and called 911, police said.

"I won't get into detail about that, but I did see things I shouldn't have," Gomez said. "I'm a father. I have a 6-year-old daughter. What I saw was not OK."

San Jose police, with the help of a security guard, arrested a 70-year-old man this week on suspicion of kidnapping and molesting a 13-year-old girl that he was hired to drive home from school, according to the police department. Sonja Shin reports.

Nguyen was booked into Santa Clara County jail on charges of felony kidnapping, false imprisonment, digital penetration with a child under 14 years old with force and lewd act with a child under 14, police said. It is not clear if he has an attorney.

Officers responded to a weapons call at Capitol Expressway and Tuers Road in San Jose at about 3:35 p.m. Monday. Gomez called 911 to report he interrupted a suspect sexually assaulting the girl, police said.

"I told him, 'You need to step out of the vehicle,'" Gomez said. "He refused. That's when I drew my weapon and I had him step out of the vehicle. He came out. I handcuffed him properly and called San Jose PD."

Gomez said the girl was in shock.

"I go, 'Are you OK?'" Gomez said. "She just gave me a blank stare and she just said, 'No.'"

The investigation revealed the victim's family hired Nguyen several years ago to drive the girl home from school, police said. On Monday, Nguyen dropped off other children, and the girl was alone in the suspect's vehicle as he drove her home.

The suspect deviated from the route and parked behind a business in the 1000 block of East Capitol Expressway, police said. Gomez approached the suspect's vehicle and observed the attack as well as the victim fighting off her attacker.

Anyone with information about the case or similar incidents involving Nguyen should contact Detective Ed Sandoval or Detective John Tran of the San Jose Police Department’s Sexual Assault Investigations Unit at 408-277-4102. Those wishing to remain anonymous may call the Crime Stoppers Tip Line, (408) 947-STOP (7867).