Inside Texas Doctor’s Plot to Kill Rival Doctor in Love Triangle

— -- Richelle Shetina thought she'd found the perfect partner in dance and in life when she started dating Joseph Sonnier.

"I loved the way that he made me feel. I absolutely loved it," Shetina told ABC News' "20/20."

But their relationship came to a tragic and abrupt end when Sonnier was found murdered in his own home.

In a case involving a love triangle and a jealous lover, police got their biggest break in solving the murder thanks to a tip from the killer's houseguest.