Poisoning is being blamed for the death of a golden eagle, the body of which was found by a walker between Banchory and Braemar in Deeside, Scotland.
Police suspect the bird was killed by a gamekeeper intent on protecting grouse. Analysis by the Royal Society for the Protection of Birds found the remains of the bird contained carbofuran, a banned pesticide.
Dave Dick of the RSPB is quoted on The Scotsman website as saying: "The poison is totally banned from use and it's an offence to even posess it."
"It seems incredible to think that anyone would want to harm such a beautiful and rare bird – but I can assure you that people would go to great lengths to protect game."
PC David MacKinnon, a wildlife crime officer with Grampian Police, said: "All crimes against wildlife are disappointing, but this incident is even more so due to the species involved.
"Based on the low population of these specially-protected birds, this incident will have a significant effect on the population."
The law provides a maximum six-month jail sentence or £5,000 fine for harming golden eagles.
Hillwalkers are being asked to be on the lookout for dead birds of prey or poisoned baits and to report them to the authorities.
PC MacKinnon says the eagle may have had chicks and its mate would have taken flight when it went missing.He said: "We are treating this very seriously – I have been involved in wildlife crime for ten years and this is only the second case of a poisoned golden eagle I have come across. There will be people who will know what has been going on and we will investigate this rigorously."