I just moved and found out this is how my neighbor is living!! He is all alone, doesn't leave the blighted house, the house is pitch black except for one lit window. His son visits to check on him every couple of weeks.
Have you spoken with any of the other neighbors about the situation? I'd find out if anyone has a relationship with the son or if anyone has called APS.
I wouldn't jump to any conclusions. You can't assume that it is within the son's power to move his father out of there, for a start. Give it a bit longer, keep an eye open - very kind and neighbourly of you - and see how things develop. There is almost certainly more to this situation than can easily be solved.
Have you spoken with any of the other neighbors about the situation? I'd find out if anyone has a relationship with the son or if anyone has called APS.
There is almost certainly more to this story.