I would agree with mollyredone, but would go further,
Not only do you need to record everything you say to him (and get him to counter-sign the record), you need to record everything you tell your own seniors, and get THEM to counter-sign what you have told them. THIS PERSON IS DANGEROUS. You, as a conscientious employee, should not have to take responsibility for this person, but, if the worst happens (and it well could), you want to make certain that you are not held responsible in law, but that the finger is pointed in the right direction. If you get your own seniors to counter-sign your written concerns, you will, not only be protecting your own future, but will also cause them sleepless nights until they do something about the situation.