By David Schwartz

PHOENIX (Reuters) - A 23-year-old man suspected of killing eight people over seven months in a string of serial shootings in Phoenix in 2016 is already behind bars on a murder charge for another slaying the year before, the city's police chief said on Monday.

Aaron Saucedo of Phoenix was arrested in April and later charged with murder in connection with the first of the killings, which occurred in August 2015, Phoenix Police Chief Jeri Williams told reporters at a news conference. The 61-year-old victim, who was shot in front of his home, dated Saucedo's mother.

Saucedo, who has been in custody since April, pleaded not guilty to that charge.

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Williams announced Saucedo has been linked to eight other shootings, bringing to nine the total number of killings investigators linked to him.

Saucedo faces the possibility of more than two dozen criminal charges, including murder, attempted murder and aggravated assault, Williams said.

Two people were injured in the shooting spree, which police said lasted from August 2015 to July 2016.

Police gave few details on how they linked Saucedo to the killings and they did not say why the attacks stopped last July. But they said in a statement the evidence includes surveillance video, witness statements and ballistics material.

One tipster could receive a $75,000 reward for information leading to the arrest, police said.

An attorney for Saucedo did not return a call seeking comment.

Investigators initially believed a serial shooter was responsible for seven deaths last year, but in recent weeks they determined two other victims - the one killed in August 2015 and another person slain in January 2016 - were shot by the so-called "serial street shooter" who they believe to be Saucedo.

"Our hearts go out to the surviving families," Williams said. "Today we are closer to providing them the justice they deserve."

While Saucedo knew the first victim killed in August 2015, the other slayings appear to have been random, police said.

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The street shootings occurred late at night or early in the morning, mostly on the west side of Phoenix.

In the most deadly single attack, two women and a 12-year-old girl were shot to death in front of a home before dawn on June 12, 2016, police said.

The Maricopa County attorney will review the case to determine which charges to formally bring against him.

The Federal Bureau of Investigation took part in the probe.

(Reporting by David Schwartz in Phoenix; Writing by Alex Dobuzinskis; Editing by G Crosse and Lisa Shumaker)