Complex sentence: Keller was first involved in controversy in 1996 when she wrote her first major opinion which denied a new trial to Cesar Fierro who had confessed to murdering an El Paso cab driver.
Split into simpler sentences: Keller was first involved in controversy in 1996 when she wrote her first major opinion. The opinion denied a new trial to Cesar Fierro, who had confessed to murdering an El Paso cab driver.