A Crime Stoppers tip led police to Lopez. Police say the victim positively identified him.
Police are also questioning Lopez's brother. They say he fits the description of the man who held the girl down during the attack.
"This is not them, whoever did it," said Josephine Lopez, the suspect's sister-in-law, while holding a sketch of the second suspect. "There's proof that this man here was working. There's proof."
Relatives say both Lopez and his brother are illegal immigrants.
Lopez is now charged with sexual assault and is being held at Harris County Jail on $35,000 bond.