If I roll a crit on a sleeping target with assassinate, do I roll 4x dice?

If I roll a crit on a sleeping target with assassinate, do I roll 4x dice or is it multiplicative and I roll 8x? What happens to their body when I hit?

— Uriah Belletto (@DarkSlayerKi) April 13, 2018

Funny rules loophole: if you roll crit on a sleeping target with assassinate, you roll all of the dice you have. However, killing a sleeping person makes you a real turd, when you think about it (see the Player's Handbook for discussions on turds). #wrongDnD #fakeJeremy https://t.co/bsUUW3GztG

— spoilers swag (@katewelchhhh) April 13, 2018