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Police hunting a serial killer in Phoenix, Arizona, thought his string of crimes had ended in mid-June when he ambushed and fatally shot two women and a 12-year-old girl in their driveway.

But investigators announced Wednesday that they have added a ninth shooting to the pattern — a July 11 incident in which the gunman fired at a man and a 4-year-old boy sitting in a car. Neither was injured.

The new incident means that the shooter — who had already murdered seven people — tried to kill again even after police had put the city on alert.

"The threat is still alive," Phoenix Police Sgt. Jonathan Howard said on Friday.

"We don't want to see anybody else get hurt. We want to make an arrest and stop this," he added. "We're fortunate in this new incident that nobody was injured."

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But, he added, "if there can be a benefit to something like this, it's that we did obtain additional evidence."

Based on witness statements, detectives now believe the suspect has access to several cars — one appears to be a white Cadillac or Lincoln, and the other is a late '90s or early 2000s 5 series BMW.

Police released this sketch of a suspect in a series of killings in Phoenix. Phoenix Police Department

Howard said investigators have looked into whether the gunman works as a mechanic or on a used car lot. The motive for the shootings remains as elusive as his name.

"Why? Why? I know I'll never understand," said Sylvia Ellis, whose daughter Stefanie and granddaughter Maleah were killed in a June 12 shooting.

She asked for anyone with any information about who the suspect might be to contact police.

"Help us," she said. "We don't want any more lives lost. He needs to be caught."

Although police have added several shootings to the pattern since it was originally announced, Howard said they are "pretty confident" they now have uncovered all the reported incidents.

In each case, the victims were attacked near their car or home, in the evening or very early morning hours, in the working-class Maryvale section of Phoenix.

Law-enforcement sources say there is physical evidence tying the shootings together.

The earlier shootings include: