A mother claims her disabled daughter was molested at a Houston Independent School District school.

The woman filed a federal lawsuit alleging the sexual abuse followed months of abuse while her daughter was a special education student at Westbury High School.

The lawsuit is against the school and an unnamed employee, who the woman claims abused her daughter but was never charged.

The mother said her daughter uses a wheelchair and is unable to walk, talk or feed herself. She wears a diaper and requires around-the-clock care.

The girl was 15 years old when she attended the school in the fall of 2009.

"Bruises started in October," the mother said through a translator.

The mother said she asked school officials why her daughter was coming home with bruises on her arms and legs. She said they told her it must be happening at home.

Denying that, the woman took her daughter out of school for two months, but she was forced to re-enroll her in January 2010. Within a few days, the mother said she discovered another bruise on her daughter's cheek and something worse.

"When I took her home that day and went to change her diaper, there was blood on her diaper," the mother said through a translator. "That's when I took her to the pediatrician."

At the hospital, doctors discovered the girl suffered some sort of sexual abuse. An investigation by the Texas Department of Family and Protective Services reached the same conclusion. Neither child welfare workers nor police have been able to identify a suspect, so the mother is seeking justice with a civil lawsuit.

"I don't want this to happen to other children because, like her, they cannot defend themselves, they cannot talk for themselves," the mother said through a translator.

The lawsuit was filed last week. The school district has not commented on the allegations contained in it.

Houston police spent several months interviewing witnesses and collecting evidence, including a rap kit and clothing. Police said all the evidence has proved inconclusive.

The girl's mother placed her daughter in a school in another school district. She said she's doing fine there.