The Colorado Fraternal Order of Police is up in arms after protesters vandalized Denver's memorial to fallen officers on Saturday during a march (above), and it wants Police Chief Robert White to resign over the matter. 

Officers were ordered not to directly confront the protesters in the heat of the moment as they poured red paint on the monument, KUSA-TV reported.

White called Saturday's vandalism "abhorrent," but said "I believe the decision we made was appropriate."

"We know who these folks are who were there on Saturday," [Denver Mayor Michael] Hancock said. "They're looking for a confrontation."

Two suspects were arrested, and DPD tweeted their mug shots.

In an open letter to Mayor Michael Hancock, the union also demanded the resignation of the city's Director of Public Safety, Stephanie O'Malley.

While it was organized professional protestors that perpetrated this planned hate crime, the blame lies completely at your doorstep. The “stop-and-wait” strategy that has become the standard DPD response to protests over the past several months developed by your Manager of Public Safety’s office and Denver Police Administration, fully endorsed by Director Stephanie O’Malley, Chief of Police Robert White, and yourself allowed this despicable hate based act to occur. The fact that Denver police officers working that demonstration had to watch the outrageous vandalism to this revered memorial without being able to intervene is shameful, inexcusable, and unacceptable. Your office and administration needs to accept responsibility for that.

DPD also tweeted out a photo of the vandalized monument:

The vandalism came during a protest march against lethal police tactics. The mayor says he stands behind White and O'Malley's decision.