A Lincoln woman told police Saturday that her 15-year-old son had sexually assaulted her foster daughter the night before.

About 8:45 p.m. Friday, the girl was in bed when the woman checked on her son, according to Lincoln Police Officer Katie Flood. The woman told police her son's bedroom door was open and she called out to him but he did not answer. She told police she heard the door to her foster daughter's room closing.

When the woman went up the stairs to see what was going on, she found her son on the hallway floor, face down, in front of the child's room.

The woman told police the next morning that the foster child said the 15-year-old had touched her inappropriately, Flood said.

The girl was interviewed at the Child Advocacy Center, describing the incident in greater detail. At this time, Flood said, police believe this was the first and only time he had violated her.

On Monday afternoon, the boy was taken into custody and lodged at the Youth Assessment Center for first-degree sexual assault of a child.