Firefighter Harper, 23, died at 1:30 a.m. local time Sunday while fighting a mulch fire in west Phoenix, The Arizona Republic reported Monday.
Harper, a newlywed, was crushed between two emergency vehicles while readjusting equipment. He died at St. Joseph's Hospital and Medical Center.
Two hours after Harper's accident, police officer Raetz, 29, died after he was hit by a hit-and-run driver while investigating a driving-while-intoxicated crash, the newspaper said.
Raetz was transported to the same hospital, where he died.
The hit-and-run driver was still at large, the Republic said.
"It is on days like this that we are reminded of the ultimate sacrifice some of our women and men make as they protect our community," Vice Mayor Bill Gates said. "It is truly a sad day when we must say goodbye to two of our finest."
Flags were flown at half staff to honor the two first-responders.