Just wondered if you'd given him a verbal warning before? This is usually done as a first reprimand. If a further misdemeanour occurs then its a written warning. Of course if there is more than one issue at the moment you could do verbal for the first and written for the second. Also, you must never state in writing that this person has been stealing unless they have been found guilty through the judicial sysem. I used to be an Adjudication Officer at the Jobcentre and Employers had to be asked to retract such statements due to libel and slander laws. This also means you cannot disclose what has happened if another employer asks you for a reference. If you are in doubt ring ACAS, they will advise you on the law and correct procedure. Good Luck