Very little is known about Martinez, other than he started working for the U.S. judicial system and eventually rose to the rank of Assistant U.S. Attorney.
Martinez was assigned to prosecute Reid, the prime suspect in the murder of a Mexican-American woman named Nadie Ramos in Mexico. He calls Reid's attorney, Fiona Duncan, to inform her that he is interested in giving Reid a plea bargain: he pleads guilty to a lesser charge of involuntary manslaughter in exchange for a sentence of two to five years in prison, instead of twenty-five to life on a murder conviction. However, Reid turns it down. Later, Martinez receives word that the murder weapon has been found, that it is the same one that cut Reid's hand, and that it has his fingerprints on it. Because of this, he offers another plea bargain of five to ten years in prison, but Reid turns down the offer again.
Eventually, the case goes to court. Fiona does her best to defend Reid by telling Judge Willa Frost about his schizophrenic mother who has Alzheimer's disease and Reid being an FBI agent for over a decade. However, Martinez counters her argument, saying that Reid violated federal protocol by sneaking across the border without notifying the FBI. Frost takes Martinez's side and denies Reid's bail.
Martinez reappears when Prentiss has a meeting with Frost at the courthouse. Prentiss tells Frost that new evidence indicates that Lindsey Vaughn was responsible for Nadie's murder since her fingerprints were found at a new crime scene, but Martinez says that these are all theories. Eventually, Frost dismisses Martinez's arguments and has Reid released from prison when the evidence is reviewed.