None of the three suspects will be charged with killing of two protected birds of prey at a royal estate.
None of the suspects was identified.
Prince Harry and a friend were in the area at the time of the shooting on Oct. 24 at the Sandringham estate in eastern England. Royal officials say the prince had no knowledge of the shooting.
"Norfolk Crown Prosecution Service has advised Norfolk Police there is insufficient evidence to prosecute anyone over the shooting of two hen harrier birds, a protected species, at Sandringham on Oct. 24, 2007," the prosecuting agency said.
"The bodies of the hen harriers have not been found and there is no forensic or ballistic evidence. Witnesses also heard unexplained shooting in the area before the three suspects said they were present at the scene, so other people cannot be ruled out.
"The three suspects, who were interviewed by police, all denied that the birds were killed by them," the agency said.
The Royal Society for the Protection of Birds said it was disappointed there was insufficient evidence to proceed with the investigation.
"We regard the killing of hen harriers as one of the most serious of wildlife crime offenses. We would always hope that people killing hen harriers are brought to justice," the group said in a statement. "We believe the illegal killing of hen harriers is the reason for this birds low UK population, especially in England where only 20 pairs remain."
The Royal Society urged Britain to spend more money on investigating and prosecuting wildlife crime offenses.