Extra patrols from the Walnut Sheriff's Station and LAPD have been ordered for the quiet residential city, which is home to a large number of current and former LAPD officers, including LAPD Chief Charlie Beck, said Mayor Mary Su.
"We do have a lot of police and sheriffs (deputies) who live in Walnut," said Su, who gave the order to lower the flags in Quan's honor.
Dorner, 33, is also suspected of killing a Riverside police officer and seriously wounding another in an ambush Thursday at a stoplight.
Quan, 28, is the daughter of retired LAPD Capt. Randal Quan, who was mentioned in Dorner's rambling manifesto pasted to his Facebook wall, and was a possible target in an alleged killing spree of people he believes did him wrong. Randal Quan represented the suspect before a disciplinary board shortly before Dorner lost his job with the LAPD in 2008.
"I will bring unconventional and asymmetrical warfare to those in LAPD uniform whether on or off duty," Dorner wrote. "You will now live the life of the prey."
Randy and Sylvia Quan live in Walnut, confirmed Su.
The Quans' daughter played basketball at Walnut High and also played AYSO soccer at Walnut Ranch Park, remembers City Councilman Tom King, also a former LAPD detective.
"No words of consolation can properly console Randy and Sylvia Quan with the tragic loss of their daughter," King wrote in an email to the city manager and his colleagues on the City Council.
He said Randy Quan briefly worked for him at the LAPD, but was then promoted to captain. King worked in the detective bureau. King said "Randy ... was a strong advocate for fairness and justice, always a professional. I cannot imagine the grief that he and Sylvia feel.
"As long as I remember they were cheering Monica as she made a name for herself at Walnut Ranch Park playing in AYSO and at Walnut High as a star athlete," King said. "I remember them always cheering `Go Monica!' from the sidelines," he recalled.
King called the suspect "a coward" for ambushing police officers and "not having the guts to turn himself in."
Su said the city sent the Quan family condolences and flowers through an intermediary. The family is not speaking to the media.
The Associated Press contributed to this report.