If someone was convicted of a crime, we can say so. "The district court of (blank) found Mr. X guilty of murder in the first degree. He was executed on (this date)."
 
The Wikipedia doesn't say there is no such thing as terrorism. Rather, it acknowledges that different sides have conflicting ideas about what constitutes terrorism. Some people use the word to mean "unjustifiable violence". Naturally, in a war or similar conflict there will be sharp disagreements on what is justified or unjustified.
 
Ed Poor