Port Isabel police have arrested a man who allegedly threatened to sexually assault his victim's younger sister if she didn't have sex with him.
According to investigators 44-year-old Juan Varela-Ruiz started abusing the girl when she was just 16 years old in 2010.
The abuse stopped in October of last year when the victim, now 18, made an outcry.
The victim told investigators Ruiz forced her to have sex with him by threatening to hurt her sister.
Police said Ruiz admitting to have sex with the girl and said knew it wasn't right.
Ruiz was charged with continuous sexual assault of a child.
Investigators told Action 4 News that Varela-Ruiz is a Mexican national.
He remains in custody at the Cameron County Jail where U.S. Immigration & Customs Enforcement (ICE) agents have filed an immigration detainer against him.