Sligo to Derry bus —bag mix up

My fiancé was on this bus tonight (it was the 7pm bus from Sligo but only left about 8) and got off in Derry. His bag was a medium sized navy canvas suitcase with an Apple Mac laptop inside. He picked up the last case when getting off, but only discovered it wasn’t his when he got home. The case he picked up is identical from the outside and contains men’s clothes. He’s very keen to get his one back and can offer a reward.