Giselle Diwag Esteban was born on February 4, 1984, in Union City, California. She attended high school in San Diego, where she became friends with Michelle Le. Esteban later attended San Francisco State University, where she introduced Le to her friend, Scott Marasigan. Marasigan and Le briefly dated before ending their relationship. Esteban and Marasigan began dating in 2003, and their relationship resulted in the birth of a daughter in late October 2005. The couple lived together for three years before separating. Following their separation, Esteban became increasingly suspicious of Marasigan's friendship with Le, leading to accusations and confrontations.​

On May 27, 2011, Michelle Le, a 26-year-old nursing student, disappeared from the Kaiser Permanente Medical Center in Hayward, California, during a class break. Her locked car was found the next morning, containing bloodstains later identified as Le's. Surveillance footage and cell phone records placed Esteban at the scene during Le's disappearance. Esteban was arrested on September 7, 2011, and charged with Le's murder. 

Despite the absence of a body at the time of arrest, substantial evidence, including DNA and surveillance footage, implicated Esteban. Le's remains were discovered on September 17, 2011, in a remote area near Sunol, California. Esteban's trial began on September 17, 2012, and on October 29, 2012, she was convicted of first-degree murder. She was sentenced to 25 years to life in prison on December 10, 2012, and is eligible for parole in 2037.​