I am building up a beater bike from garbage finds. I'm only missing brakes, a chain, and a cassette.

Last night, while meandering through some trash, I found a busted wheel that had a seemingly functional 5-speed cassette on it. The cassette said "Shimano DG," which I've found no info about online. I took the whole wheel home, and tried to take the cassette off with my cracker. The hole was a little to small for it to fit in, however.

Anyone have any ideas on how else I could get it off? I don't mind destroying the wheel, it is already damaged.