The shooting deaths of Officers Eric White and Jason Wolfe marked the fourth time since 1970 that the Phoenix Police Department has lost two officers in one day.
Crime researcher Steve Varner, son of a slain Arizona lawman, said multiple police killings have taken place all too frequently in Arizona and the rest of the nation.
Just this year, in addition to Phoenix, there have been multiple killings in Athens, Ga.; Detroit; Birmingham, Ala.; and Bradford County, Pa.; all of them shootings, Varner said.
"The death of an officer always hits you hard, but these kinds of cases always seem to hit you harder," Varner said.
Varner, 44, a west Phoenix resident and retired Air Force master sergeant, does research for Officer Down Memorial Page Inc., a Web site that keeps track of U.S. peace officers who have lost their lives in the line of duty.
His father, Robert William Varner Jr., 51, a Navajo County sheriff's deputy, was shot dead Dec. 31, 1988, after making a stolen-vehicle stop.
Steve Varner said three Graham County lawmen were gunned down Feb. 9, 1918, marking the darkest day for Arizona peace officers.
Sheriff Robert F. McBride and two deputies, Kane Wooten and Martin Kempton, lost their lives during a gunfight at a cabin in the Galiuro Mountains in southern Arizona.
Varner said there have been double killings involving other Arizona police agencies, including the Arizona Department of Public Safety and the Maricopa County Sheriff's Office.
The string of double police killings in Phoenix began Dec. 28, 1970, when Officer Albert R. Bluhm was shot dead outside a Phoenix motel.
A second officer, Dale C. Stone, lost his life during a motorcycle crash while responding to a call to assist Bluhm.
Less than a month later, Stone's father, Rex Stone, a Maricopa County sheriff's deputy, was shot dead with another deputy, Warren LaRue, while serving legal papers.
On July 1, 1982, two Phoenix officers, Ignacio G. Conchos and John R. Davis Sr., were fatally wounded while searching for bank robbers.
Conchos died that day; Davis died of wounds a month later.
On July 26, 1990, two Phoenix police sergeants, John Domblisky and Danny Tunney, were killed in a head-on crash when a motorist, an attorney suspected of driving under the influence of cocaine, crossed over the traffic median and into the path of their vehicle.
White and Wolfe, the latest victims, were the second and third Phoenix police officers to lose their lives this year.
Officer Don R. Schultz, a police diver and 20-year veteran, died May 12, two days after being pulled from a canal during a diving operation in which his breathing device came off.
Detective Tony Morales, a police spokesman, said Phoenix officers are taking the shooting deaths of White and Wolfe especially hard.
"This is the worst I've ever seen," Morales said. "The shock and grief that you can see and feel throughout the department is just pretty obvious."