I just...think this letter is great.

Dear Class,

Unfortunately there was an incident of cheating on today's midterm. Before I contact the person who is at fault. I would like to give you the opportunity to come forward. There will be consequences either way, but they might be reduced if you email me ASAP!

Remember that cheating is insulting to me, your classmates, and your own abilities. It can affect your grade and position at BU. I am willing to work with everyone to understand these concepts and feel good about their grades- but I expect the same diligence in learning the material in return!

If this email relates to you WRITE ME BACK ASAP!

Sincerely,
Chelsea Shields Strayer

The reson I like it is this: you get kicked out of school for cheating.
For gds sake, proofread it!
and don't use so many exclamations, it's just rubbing your nose in other's imminent doom.