entity in the building?

So, there is a two-storey barrack in front of my house. People used to live there, and now it's possible too, but for more than six months no one has turned on the light there (ever) and one of the windows is permanently open, although it happens outside -30C or more.

Yesterday, the light turned on in one of the rooms and im could watch for a few minutes as some kind of shadow walks in different directions near the window. It doesn't look like normal human movement, rather like running erratically in one place.

when I went to the window to look at it, it seems that he jerked sharply and also seemed to come to the window. After a couple of seconds, he turned off the light. Even later, he turned it on again, then turned it on in the hallway and did not manifest himself. After that, he turned off the lights in the room and then in the hallway, after which the activity stopped.

I have no idea who it could be. There are no traces of this house, but if someone spent more than a few days there without leaving, why didn't he turn on the light earlier? And anyway, why is the only time he needed light is 4:30 am?

clarification - I do not know if anyone lives there now. I don't see anyone who went to this house, except for a fat man who appeared there several times two weeks ago, but when he's around, he parks his car near the house. He hasn't been here these days.

What do you think it could be? It's not such a bad and ruined place that homeless people happen to be there, but it's also impossible to imagine that this is a normal person. Maybe a poltergeist?