Gardaí say they are disgusted by the attack on the plaque, put up in Co Donegal by the heartbroken family of the late Gda Gary McLoughlin.
The 24-year-old garda died when he was struck by a car in Burt, Co Donegal, on December 14, 2009.
Martin McDermott, who had more than 80 convictions when he killed Gda McLoughlin, was later sentenced to seven years for his manslaughter.
The plaque was erected at the scene of Gary’s death at Lisfannon, Burt, by his family last year.
The plaque reads simply: “For some moments in life there are no words.”
However, gardaí believe on Monday night or early Tuesday morning, the plaque was smashed to pieces.
One piece was taken more than 25km to the home of Grda McLoughlin’s girlfriend, Shauna Bradley, at Drumfries, Buncrana.
The vandals left the piece of the plaque on the bonnet of a disused car belonging to a family member and also sprayed “RIP” on the piece of the plaque.
Garda Superintendent Kevin English said he and all members of An Garda Síochána are “sickened and disgusted” by the mindless attack. “I have no words to adequately describe what happened,” he said. “It was sick, vile, and sinister in the extreme, and it has caused untold hurt to the family of Gary, the community and all his colleagues.
“It is a depraved act carried out by people who have no respect for anyone and it is a direct attack on Gary, his family and An Garda Síochána,” he said.
Supt English said Gda McLoughlin’s parents, Noel and Una, are devastated by what has happened and cannot understand why someone has done this to the memory of their youngest son.
Garda Supt English said: “These people not only removed the plaque but also sprayed graffiti on it. I don’t know how anyone can stoop so low. I don’t know how much more this family can take.
“They have endured the loss of their son, a criminal trial, and then the escape of Martin McDermott. All they ask is time to grieve for their unnecessary loss.
“I would ask people to come forward and I am confident that whoever did this is from the local community.”