Warning: Below there is a graphic image of the shot bird in this article
Wildlife experts have warned that the rare red-footed falcon in the Cambridgeshire Fens is "not an isolated incident".
The protected bird of prey was found dead found dead near Whittlesey last month. An X-ray confirmed it had been shot.
The RSPB has warned that birds of prey being are killed in the British countryside almost every week.
The Bedfordshire-based charity is offering a £1,000 reward for anyone who has information on the shooting of the falcon.
Last year there were 91 known birds of prey victims in the UK. Of those, 15 were in the East of England.
In what was described as one the "worst cases" of bird poisoning in the country, last November gamekeeper Alan Lambert was found guilty of killing 10 buzzards and sparrow hawk in Holt, in north Norfolk.
The Stody Estate, where he worked, is still paying for his actions. This week it was announced they would be losing £200,000 of farming subsidies.
The RSPB is encouraging members of the public to report dead birds of prey to them.
Specimens are brought the evidence room at the charity’s headquarters in Sandy, Bedfordshire. Experts examine whether they have been illegally killed. If so, police become involved and investigations begin.
Click below to watch the full report from ITV Anglia's Claire McGlasson.