Do I send co-signer copy of complaint letter also?

[Deb Smith]

I received a phone call from the neighbor of my tenant with a pretty long list of complaints. And they're definitely not just being petty. They've had to call the cops on them for loudness at 2AM,  a man urinated in their front lawn (townhouse with child in home) smoking Pot inside unit (lease says no smoking), lots more. 

I'm sending a letter to my tenant. 

 Do I send the co-signer a copy of the letter also?  This is my first tenant with a co-signer. And while I'm at it should I always CC the co-signer for everything, even late notices or is it a case-by-case situation?