A 39-year-old Waianae Valley man is in police custody after assaulting and holding his girlfriend against her will for nearly 20 hours yesterday.

After suspecting the victim of infidelity, the man supposedly prevented her from leaving their home, and then assaulted her, police said. She was detained from about 2 a.m. to 10 p.m., police said.

The woman was taken to the hospital with undisclosed injuries.

The man was arrested at the scene and is being investigated for kidnapping, assault and terroristic threatening.