review of the english language, when using the indefinite articles of a or an the choice of which one to use is determined by whether the noun modified by the article begins with a vowel or a consonent. In this case the noun being modified is leo, an abreviation for law enforcement officer. "l" not being a vowel means that one would use a instead of an to modify a noun begining with the letter l. A lesbian or a litterbox, not an lesbian or an litterbox or an leo.
