Tenant Moving Out B4 Lease End and Landlord can Keep Security D

[Peace Lily]

Dear BP Members,

Tenants moved out before lease ended and said that I can keep the Security Deposit even though SD didn't cover all the trash they left and one month short rent. Is there official email I should send to protect myself keeping the SD so that we can officially end the lease early? I do not want they regret later and said that I didn't return the Security Deposit to them. Please advise. Thank you!