Prosecutor Juan Martinez said in court records that the death penalty was being sought because the killings were committed in a cold and calculated manner.
Thomas Glow, an attorney representing Saucedo, declined to comment on the plan to seek the death penalty against his client.
Saucedo has pleaded not guilty to charges of first-degree murder, attempted murder and drive-by shooting in attacks that killed nine people and wounded two others during a nearly one-year period that ended in July 2016. At court hearing in May, Saucedo declared that he was innocent.
Investigators said the victims were shot by Saucedo as he prowled the neighborhoods in a car and opened fire from inside it or stepped out briefly to shoot before driving away. The victims were outside their homes or sitting in cars during the attacks.
Most of the killings were in a mostly Latino neighborhood.
Police said the victims included a 21-year-old man whose girlfriend was pregnant with their son and a 12-year-girl who was shot to death along with her mother and a friend of the woman.
Authorities say a 9mm shell casing was found in Saucedo’s car when it was seized by police. Police said the casing was fired from the same gun as the shells found in the aftermath of nine of the 12 attacks.
The killings stumped investigators for months, but they got a break in April when Saucedo was arrested in the August 2015 fatal shooting of 61-year-old Raul Romero, whose girlfriend was Saucedo’s mother.
It was unclear whether prosecutors are seeking the death penalty against Saucedo in Romero’s death.