MARYVALE, Arizona (CNN) -- Could a suspected serial killer in Phoenix have been stopped after his first victim -- and before he allegedly killed eight other people?
Authorities in Arizona say Aaron Juan Saucedo killed his mother's boyfriend, Raul Romero, in August of 2015, and later randomly killed eight more people in a series of shootings in 2016.
Unbeknownst to authorities, the weapon used to kill Romero was among eight guns seized from several Phoenix-area pawn shops in September of 2015 as investigators searched for a suspect in a separate case in which someone shot at random cars on Interstate 10.
But the weapon now known to be connected to the Romero killing ended up not being analyzed. Authorities found a possible match for the highway shootings weapon in their examination of four of the weapons, so they didn't further test the other guns and returned them to the pawn shops.
In January of 2016, Saucedo allegedly began randomly gunning down people in a Phoenix neighborhood, killing eight more victims.
Random shootings in Maryvale
It was about a year ago, police say, that Saucedo targeted the low-income neighborhood of Maryvale, standing outside a car mostly at night and shooting people with a semiautomatic pistol.
Most of the shootings happened as victims walked down the streets or stood in their yards. On June 12, 2016, a 12-year-old girl and two women in their 30s were shot dead as they stood outside a house.
As frenzied law enforcement agencies searched for answers, fear struck at the heart of the community.
The first victim
Months before he allegedly targeted Maryvale, police say Saucedo's first victim was his mother's boyfriend, Raul Romero.
Saucedo, 23, was arrested in April and charged with Romero's death, the complaint filed with the charges showed. Saucedo denies any involvement in the 61-year-old's death, the documents said. He remains in custody, and it's not clear if he has a lawyer.
As the investigation into that killing gathered more evidence, Saucedo was charged in May with an additional 26 felony counts -- including multiple murders and drive-by shootings -- in connection with the street shootings, authorities said. Officials have not discussed a motive in the random killings.
Probe in separate case turned up murder weapon
The gun allegedly used by Saucedo in Romero's death was found (although authorities didn't know it) during the investigation into another crime: a series of drive-by shootings on Interstate 10 in August and September of 2015.
The weapon that appeared to be a match for evidence in the highway shootings case had been pawned by Leslie Merritt, said Trooper Kameron Lee of the Arizona Department of Public Safety.
Merritt was arrested and charged with 16 felony counts in the Interstate 10 shootings that left several people wounded, but no one was killed. On September 21, 2015, the Department of Public Safety returned the other seven weapons that had been seized to their respective pawn shops.
Merritt, who consistently said he was not involved in the highway shootings, spent seven months behind bars before a Maricopa County judge ordered he be released, and the charges against him were dropped a few days later. The dismissal came after a motion by Merritt's attorneys that cast doubt on the ballistics evidence.
Raul Garcia, a spokesman for the Department of Public Safety, says the freeway shootings case -- which is not linked to the Maryvale street shootings -- is still open.
Merritt's gun and the weapon allegedly belonging to Saucedo were both pawned at the same shop, according to Garcia. But that's as far as the connection goes, he said.
Why wasn't gun linked to Saucedo tested?
Lee defended the decision in 2015 not to analyze the gun allegedly belonging to Saucedo, saying it's standard procedure.
"We stopped analyzing the rest of the weapons because we found the one we were looking for," he said.
And it doesn't appear that the weapon that was returned to the pawn shop in 2015 was used by the suspected serial killer. Court documents filed in the murder case against Saucedo said the suspect sold the weapon linked to Romero's killing to a pawn shop on September 1, 2015. Authorities investigating the highway shootings seized that weapon and others on September 17, tested some of them, and returned them to the pawn shops on September 21, 2015. The pawn shop sold the gun on June 28, 2016, the court documents show, and police later retrieved the gun from the new owner to conduct ballistics testing. That testing showed the weapon was used in the Romero murder, the documents said.
A neighborhood relieved, lawmaker concerned
Maryvale flower vendor Scott Annesley, 57, said he's more relaxed since a suspect was arrested in the neighborhood shootings. Before the arrest, he said, he'd look over his shoulder a lot more.
"I felt nervous because many areas of Maryvale are not well lit and there is a lot of gang activity in the area," he said.
Lydia Hernandez, a former state representative, told CNN she wanted to know why the prosecutor had sealed the case against Saucedo.
"As a Maryvale resident, we want to make sure that we do our due diligence," she told the affiliate. "I don't know what all those facts are. I know they're confidential. I'm asking for transparency. I don't want to have a false sense of security until ... we've got the right person and he's behind bars."
CNN's Sara Weisfeldt reported from Maryvale, with Faith Karimi and Alanne Orjoux reporting and writing from Atlanta. CNN's Dave Alsup and Ralph Ellis also contributed to this report.
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