Prepare your shrimp by peeling off their shells and removing their tail bits heads, saving the shells and heads.  Refrigerate your shrimp.  Add 8 cups of water and a generous pinch of salt to a large stockpot with the shrimp shells, tails, and heads, then bring to a boil over high heat.  Lower heat and simmer, partially covered, for an hour.  Let the stock cool, then strain the shells from it, saving the stock in a large bowl for later.

Heat 1 tbsp butter in the stock pot, then add the sausage.  Saute the sausage until it has browned, about 8 minutes.  Remove the sausage from the stockpot and set aside.

Heat 3 tbsps butter in the stockpot over high heat.  Add the flour and reduce heat to medium.  Cook flour and butter, stirring constantly, until roux has become medium-dark brown in color.  Add your onions to the stockpot and saute until they soften, about 4-5 minutes (we nearly pureed ours, so it didn't take long).  Add the garlic and half of the green onion and saute for another 3 minutes.  Next, add the tomato paste, thyme, salt, sriracha, chili powder, black pepper, and Worcestershire sauce to the pot, stirring to combine.  

Stir in the canned tomatoes that you have prepared how you like them - we ran ours through the food processor, liquid and all.  You could also chop or dice them, saving their liquid.  Gradually stir in the shrimp stock, then add the sausage.  Bring pot to a boil once more, cover and reduce heat to medium-low, and simmer for 30 minutes.

Add your shrimp, crab, and mussels to the pot.  Bring pot back up to to a boil and simmer for an additional 15 minutes.  Stir in your green onion and serve.