Here is the definition of a criminal from "the Free Dictionary"...on line version
"1. (Law) a person charged with and convicted of crime"

Your statement that a person is a "criminal" if they have "committed a crime before they are actually convicted" is, I presume your opinion, not the statement of any legal reference source.

We have, as you know, a presumption of innocence as the backbone of our criminal justice system.  You will note that legal documents and all media reports are very careful to respect the principle of "innocent until proven guilty."  Our court system is the venue for proving (or not proving) someone guilty of a crime and, thereby, defining him/her as a criminal.  

I may think someone is guilty.  You, or anyone else, may think someone is  guilty.  However, when applied to our legal system, that "charged and convicted of a crime" is the key factor defining a persom as a criminal.