Authorities now believe the shooter first struck on March 17, injuring a 16-year-old teen who was walking down the street at 11.30pm.
Van Zandt also said the pattern of victims, which Phoenix police have described as random, may not be random to the shooter.
The killing of 55-year-old Krystal Annette White is the additional homicide now listed by police as believed to be linked.
He may have an accomplice, police said. "We need our community to call us or Silent Witness and help us solve these cases, bring justice to these families and victims, and prevent more violence from occurring".
Law enforcement officials believe the Phoenix shootings were committed by the same serial killer, as they all appear to be drive-by incidents, perpetrated by the same suspect, without any clear motive.
June 10: A 19-year-old man, Manuel Castro-Garcia, was fatally shot in front of a friend's home on the 6500 block of W. Coronado Road when a dark sedan stopped next to him, KNXV-TV reported.
The unidentified sister said, "He had just step foot outside the vehicle, his auto door was still open". All of these people were so good.
"She rose through the ranks of the Phoenix Police Department, and has earned the respect of her colleagues and the communities she has served in every role she's had, from foot patrol to command", Phoenix Mayor Greg Stanton said in a release.
Police released a sketch of a suspect but not much else.
The wider geographic spread means all residents should heighten their awareness and be sure to report suspicious activity, said police Sgt. Jonathan Howard.
Extra officers have been added to the Maryvale area on nights and weekends, police said.
June 3, 2016: At approximately 9:50 p.m., Horacio De Jesus Pena was shot and killed in front of a home in the area of 6700 W. Flower St. Ellis later succumbed to her injuries.
As her son continues to play in the NBA's Summer League, Jeri Williams is now police chief in Oxnard, California.
Maleah's grandmother told ABC News that she had no idea the girl was even in the auto when the shots rang out. But after reviewing evidence police say the shooting deaths are linked and are now urging residents to be extra cautious because of the a wider geographical area.
There have been no related shootings since June 12.