Long time lurker but first time posting. Not sure if I am being unreasonable/paranoid about this, and more importantly, I need advice on what to do about it...
My building has five flats, I live in the top one (no lifts). My neighbour two floors down is a bit quirky (can't elaborate as worried it's too specific to him), but on the rare occasions that DP and I have encountered him, he's been perfectly friendly.
A few weeks ago, DP and I had to isolate, so we had a lot of deliveries, takeaways etc. coming in that we needed to have brought up to the top floor. I know it's not ideal, but we did try to limit it, and the delivery guys weren't any noisier than we would have been making the trips ourselves (probably less so if anything).
On three separate occasions - notably all in the evening - neighbour opened his door to challenge the delivery guy. We could hear neighbour asking them who they were, what they were doing, etc., which seemed a bit odd given that they usually wear helmets and/or a uniform/branded jacket of some sort so it's pretty obvious. Neighbour has a peephole, so surely he could've just taken a quick look, determined it was a delivery, and gotten on with his life. And these are just the occasions we noticed/heard.
Fast forward to us being out of isolation again. One night i came home around 10pm, and sure enough, he opened his door (despite having a peephole). I said hi and kept walking, but he ignored me and just kind of stared past me whilst holding the door wide open.
I was bemused at the time, but now I'm a bit worried: my keys have gone missing since I last opened my flat. They are definitely not in the flat, but I must have let myself in somehow as DP wasn't in.... what worries me is that I have a track record of leaving the keys in the external lock after letting myself in, so theoretically someone could have taken them - specifically this neighbour.
I feel silly typing this and expect to be told I'm paranoid for thinking he walked up 2 floors to take my keys (how would he even known they were there? But if he's spying on people, maybe that's just what he does?)
I genuinely feel creeped out as I can't think of any other possibilities... please tell me there is a simple answer that I am missing!