The girl was sleeping in her Hayward home around 2 a.m. Thursday when a stray bullet from drive-by shooting wounded her in the buttocks, Sgt. Mark Ormsby said.

When the girl woke up in pain and had blood in her underwear, her parents thought she had started her period, police said. They also found no indication she had been shot.

Ormsby said when she woke up for school and was still in pain, her parents inspected her bed and saw bullet holes.