HOUSTON --A man is accused of sexually assaulting a teenage girl while he was babysitting her sister. Willie Earl Gillyard Jr. is charged with sexual assault of a child under 17 years of age. According to court documents, Gillyard, aka 'Diablo,' was babysitting the 6-year-old sister of the 15-year-old victim on March 25, 2010 when Gillyard pushed the teen girl over the couch, pulled her pants down and sexually assaulted her. The documents state Gillyard stopped when he heard the 6-year-old girl approaching the room. The little girl told authorities that she saw her sister with her pants down and Gillyard sitting on the couch. Then about a month later, Gillyard was at the victim's house drinking and spent the night, court documents state. The 15-year-old said Gillyard went into her bedroom while she was asleep and sexually assaulted her. She said he threatened her to be quiet and not to tell anybody. The documents state the victim later told her school counselor. Gillyard, 39, is being held on $20,000 bond.