Travelling towards Southport this afternoon, I had my backpack on the overhead rack on the left hand side and I was sitting on the right hand side. This is because there's only a rack on one side, and I didn't want the sun in my eyes so sat across the aisle and a couple of rows back. I was checking it regularly from my seat, but became distracted because I started listening to music on my earphones to block out a noisy child opposite me. Between Formby and Freshfield I looked up and saw a space where my backpack should have been . Immediately jumped up and ran to the nearest door, where a bloke had my bag on top of his wheelie case and was about to leave the train. This chap had been sat below my bag and saw me put it up there, he also kept glancing at me during the journey, but I thought nothing of it. I said "that's my bag" and he immediately gave it me, mumbling something about "I was going to hand it in, there was a woman sitting there". I said "you saw me put it there, you knew it was mine". The doors opened and he made off pretty quickly, but not before I had got a profile picture of his head and shoulders. Quite a respectable looking bloke, probably in his 50s with short grey hair. I tweeted Merseyrail and told the gate guy at Southport, who suggested 61016 for BTP, but even if they check their CCTV they wouldn't know where to find him. I was quite shaken by that experience. Just warning people to stay vigilant if they use overhead racks that aren't immediately above their seat and in permanent view. That's on any train not just Merseyrail. On the scale of today's events in Merseyside it's nothing, but thought I would reinforce the reminder to keep your luggage with you whenever possible. I would have lost my iPad and Kindle, probably £600 to replace. Won't make that mistake again .