Story highlights David Enrique Meza, 25, is charged with domestic violence resulting in murder

A wealthy Texas retiree he'd met online was found stabbed to death in a Mexican ravine

Meza's long-term girlfriend is charged with obstruction of justice in the case

(CNN) While he's dating a young woman, a man allegedly meets an older man online. They start their own romantic relationship, one that involves trips to Mexico and a Christmas gift of a motorcycle.

Then, that second man -- a wealthy, 52-year-old Texas retiree named Jake Clyde Merendino -- was found stabbed to death in a ravine alongside a Mexican highway.

And authorities say his lover, and that lover's girlfriend, are responsible.

David Enrique Meza, 25, was arrested and charged in federal court Wednesday with one count of interstate or foreign domestic violence resulting in murder. His long-term girlfriend, 20-year-old Taylor Marie Langston, faces one count of obstruction of justice and one count of lying to a federal officer. Police said she claimed to be at a friend's house in Tijuana, Mexico, around the time of Merendino's death.

Meza and Langston also face one count each of conspiracy to obstruct justice, according to a news release on the website of the FBI's San Diego office

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