Aaron Saucedo, 23, is responsible for a series of deadly shootings in Phoenix in 2016.
The suspect had already been charged with murder in connection with a killing in August 2015, police say.
Now Aaron Saucedo has been linked to the deaths of eight other people, between January and July 2016.
Police say they have not identified a motive but believe the man acted alone. Aaron Saucedo’s lawyer has not commented.
The 2015 victim was a 61-year-old man who had dated the suspect’s mother, Phoenix Police Chief Jeri Williams said.
The other victims, including a 12-year-old girl and a 55-year-old woman, seem to have been targeted at random.
Phoenix Mayor Greg Stanton said: “Today is a good day in the city of Phoenix.”
Police gave few details on how they linked the man to the killings, which stopped last July amid extensive media coverage.
However, they said the evidence included surveillance video, witness statements and ballistics material.
Aaron Saucedo faces 26 additional felony counts, including multiple counts of homicide, aggravated assault and drive-by shootings.
The Maricopa County attorney has not yet decided which charges to formally bring against Aaron Saucedo.
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