McElroy's Boiled Shrimp

This is a recipe that was floating around the office I worked in years ago,
and I must say it is a very good one. Is it really the recipe from McElroy's
Harbour House Seafood Restaurant in Biloxi, MS? I was told so, and
perhaps it actually is. In any case, the shrimp is delicious. My first
question was - and is - where's the garlic??? Add as much as you like...

1/2 cup Zatarain's liquid crab boil
1/2 cup salt
1 tablespoon black pepper
1 tablespoon olive oil
Juice and rind of 2 lemons
1 gallon water
5 pounds headless shrimp

Place water in a large kettle. Add crab boil, salt, pepper, olive oil,
lemon juice, and rind to water. Bring to a boil. Preheat shrimp by
running them under hot water. Place shrimp in boiling water; bring
back to a boil. Remove from heat and let stand 5 minutes. Drain
and serve with cocktail sauce.
 

Cocktail Sauce

2 cups ketchup
1 1/2 teaspoons Worcestershire sauce
1 teaspoon lemon [or lime] juice
Black pepper to taste
2 tablespoons prepared horseradish
[We add minced garlic - a clove or two at least - and Tabasco]

Combine all ingredients in a container with a tight-fitting lid.
Refrigerate.