Compare values in same column grouped by serial

I have this kind of table:

Where I have some tools, every serial must have an SR (send to a job)and an AT (Maintenance the tool) interspersed. If a tool goes to a job, just to have maintenance before. 

Every tool (serial), must have an AT before an SR and after.

I would like to create a calculated column with "CRIME" if this rule is broken.

Thanks in advance.

Best regards