A three-year investigation into the killing of 16 birds of prey has ended with no result.

Four buzzards and 12 red kites were poisoned in Conan Bridge, Ross-shire, in spring 2014 using bait contaminated with illegal pesticides.

No arrests have been made despite the offer of a £27,000 reward.

On Thursday, Police Scotland said its inquiry had ended due to a 36-month time bar on offences.

Highlands and Islands chief superintendent Philip Macrae insisted "every line of enquiry" was explored.

Police do not believe the bait was set with the intention of killing birds of prey.

Detective inspector Scott Macdonald said: "I remain convinced, based on the advice of partners involved in the investigation, that the bait was laid for illegal pest control and not specifically to target the birds of prey.

"However, they became the unfortunate victims of this illegal act."

RSPB Scotland spokesman Duncan Orr-Ewing said: "This appalling incident should act as a warning to anybody contemplating using illegal poisons in the countryside as to the possible risks to red kites and other vulnerable wildlife."