Prosecutors have dropped charges against a gamekeeper accused of illegally shooting a bird of prey.
RSPB Scotland handed a video reportedly showing the killing to the Crown in June 2013.
Prosecutors decided it would not be admissible in court, however, partly because it was filmed secretly.
RSPB Scotland has written to the lord advocate seeking an “urgent meeting” to discuss the decision.
Duncan Orr-Ewing, head of species and land management at RSPB Scotland, said: “We are appalled and extremely frustrated that the court has not been given the opportunity to give a judgment based on this clear footage.
“There is little point in passing laws to protect our most threatened species if the public authorities ignore the strong public concern about the scale of wildlife crime in Scotland.”
The RSPB’s camera was monitoring a nest belonging to a pair of hen harriers on the Cabrach Estate in Moray.
The Crown Office said the RSPB had set up the camera with the intention of securing a prosecution, although the wildlife charity has denied the claim.
A Crown spokesman said: “Discussions have taken place over a number of years between RSPB and Crown about the admissibility of evidence obtained through the use of covert surveillance.
“The Crown has consistently made it clear that strict legal tests must be met before evidence which has been obtained irregularly, such as the evidence in this case, is admissible.
“We will continue to have further dialogue with RSPB.”
He added: “In the whole circumstances, Crown Counsel concluded that the evidence would not be admissible in court.
“In light of that conclusion it was entirely appropriate that proceedings were brought to an end.”