I'm not even sure if I'm asking my question in the right category.
We moved out of a house about 16 years ago and just recently my Father has indicated to me that he left something behind and wishes he could get it back now.
It was hidden in the attic where no one would really ever have to go for any reason except possibly to hide valuables like my Father did. There is a very good possibility this box is still sitting up there. Is there any way, possibly with the help from local authorities and permission from the current homeowner that we can go and get this item out of the attic?
I know it sounds crazy and I don't know why he never said anything before now.

You could politely ask the current homeowner if you could retrieve this item from their attic. If they refuse, you essentially have no recourse legally to make them hand the item over after all these years.

What is this item? If it has not intrinisic value and you can prove you once lived in the house, then talk to the current owner. If they refuse you are out of luck.

It now belongs to the current house owner, the only thing you can do is ask permission to go up there.

Well, the item is a box containing about $20,000 cash. My father had a very prosperous business and always had a "cash stash" around. He was able to pull money out of it when he needed for circumstances that arose... such as weddings, cars, furniture,etc. It wasn't illegal money. He owned a parking lot in a busy part of the city back East and that was extra money. He said he forgot it up there. I don't doubt it they always had more then enough money. But they don't now, their social security isn't enough for them to live on, and they could really use that money at this time in their lives.

I wouldn't even bother. You have mo legal right to that money. And the current owner is not likely to give. You permission once they know what it is