If you were to look up the word Convict you will find that an overwhelming number of dictionaries give the definition as
Convict 1. Declare (someone) to be guilty of a criminal offence by the verdict of a jury or the decision of a judge in a court of law.
Convict 1. Law To find or prove (someone) guilty of an offense or crime, especially by the verdict of a court:
con•vict verb (used with object)
1.to prove or declare guilty of an offense, especially after a legal trial: to convict a prisoner of a felony.
2. to impress with a sense of guilt.
Why it matters [and how it applies to the John Banks case]