According to police, Saucedo stalked victims after dark, selecting people who were either outside of their homes or sitting in cars before opening fire with a handgun.
Police notified all the victims' families Monday before publicly announcing Saucedo's arrest.
Yesterday, they announced they had arrested Saucedo, a former city bus driver, over the killings while providing scant detail about what motivated him or details about how they made a break in the case, other than to credit tips.
CBS affiliate KPHO-TV reports that Police Chief Jeri Williams said 23-year-old Aaron Juan Saucedo is linked to nine murders and 12 incidents between August 2015 and July 2016, which is three more attacks and two more murders than originally thought.
ABC15 has learned there is a possibility of more arrests in this case, but that may or may not happen.
Aaron Saucedo, 23, appeared before a judge late Monday night and acknowledged that he understood the goal of the court appearance to inform him of the allegations.
"I was beginning to think I was never going to get that phone call", Lora, 27, told NBC News. They would not elaborate, and details of the evidence assembled against Saucedo were sealed by a judge at prosecutors' request.
Deputy County Attorney Patricia Stevens filed a motion to seal the paperwork, which was granted.
The shootings stymied the authorities for months, and the police are still unsure of Saucedo's motive.
All the other killings were random, police said, and Saucedo was not believed to know his other victims, which included a 12-year-old girl.
Police linked the murder to the string of shootings. In 2015, Saucedo was taken into custody on April 19 on suspicion of killing his mother's boyfriend.
While the suspect knew the August 2015 victim Raul Romero, 61, he is not believed to have known his other victims.
A reward of $75,000 is being given out to the unidentified tipster or tipsters.
Investigators initially believed a serial shooter was responsible for seven deaths a year ago, but in recent weeks they determined two other victims were also shot by the same gunman, who they believe to be Saucedo, including the victim killed in August 2015. Authorities investigated him more closely and connected him to the serial killings.
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During the height of Saucedo's alleged killing spree, in summer of 2016, locals described West Phoenix as a "ghost town".
The Associated Press was unable to reach Saucedo's public defender on Monday. Since that time, Saucedo has been implicated in the death of 22-year-old Jesse Olivas, who was killed in a drive-by shooting on January 1, 2016.
"Our hearts go out to the surviving families", Williams said.
Authorities said they had initially focused on only seven of the fatal shootings, but police said Monday that they had tied Saucedo to all nine killings, including Romero's.
Beltran said Pena was friendly with everyone and a devoted son who liked to run, work out and read the Bible.
Castro-Garcia, 19, was shot and killed on June 10, 2016, when five of the victims were shot within a 10-day period.
Castro said she was happy a suspect has been arrested but sad because it does not mean her son will come back. Every day I would just pass by and touch it and pray, "Lord get him. The pain is the same".
She said he preferred playing basketball with friends to partying.
"The only thing I can say is thank God there's going to be justice and we leave it in God's hands".
Lora Romero said Saucedo's arrest, while a relief, reopened the wounds of losing her father - a hard-working, generous man who loved to watch football, play softball and tell amusing stories to his kids.
Smith was seven months pregnant with the couple's child when Verdugo-Sanchez was fatally shot in front of a home. "But they wanted me to find out from them and not the news".
Police say Saucedo shot at two teenage boys on March 17, 2016, striking one of them in the arm.
Marina Smith, the partner of 21-year-old Diego Verdugo-Sanchez, who was gunned down on April 1, 2016, said she welcomed news of the arrest but was still grappling with his death.
Police are hunting for a serial killer terrorizing the Phoenix area.