The piercing scream, like a sound from a horror film, triggered taekwondo instructor Simon An to draw on his years of martial arts training.

Around 4 p.m. Tuesday, shortly after the doors of his family-owned and -operated studio in Texas opened for evening classes, An and his father, his mother, his older sister and his younger brother heard shrieks coming from a neighboring business.

The family of five, each with a fourth-degree black belt, run the Yong-in Taekwondo dojo in Katy, outside Houston. They initially ignored the sounds, assuming they came from employees playing around in their break room. But then a piercing “final scream” prompted the family into action, An said.

His family ran to the store and opened a door. There they found a man on top of a young woman with his hands “in [in]appropriate places” as she attempted to fend him off, An said.

An’s father, Hong, yanked the attacker away by his shirt and pinned him to the ground. An’s sister, Hannah, grabbed the girl and rushed her out of the room while An and his brother helped subdue the attacker.

“It just happened so sudden,” said An, who has been practicing taekwondo for 16 years. “It was all self-defense. The intruder was trying to run away — scratching, biting, anything he could do.”

But An’s dad, a taekwondo grand master, held down the attacker for 10 minutes until law enforcement arrived, he said.

“My dad is strong. He expected us to protect him,” An said. “He had a lot of trust in us.”

The Harris County Sheriff’s Department has credited An and his family with saving the young woman from a sexual assault.

“By utilizing their training and discipline, they managed to stop the assault and hold him,” Sheriff Ed Gonzalez said in a series of posts on X.

The suspect has been charged with attempted sexual assault and unlawful detention, the sheriff’s department said.

“Thank you to the Yong-In dojo for your quick action in protecting others,” Gonzalez wrote.

This article was originally published on NBCNews.com