I don't think that's the case. It appears to me that the lawyer is serving his clients first by preserving the evidence of their damages. Assuming his clients prevail in their claims, any winning judgment or settlement would also mandate that all arrest records must be expunged. But first things first...
If someone were punching you, and you could physically avoid it by running away, but stood there so the damage would be worse, you are hurting your case. A plantiff is obligated to mitigate damages, in my opinion. The fact they were arrested will not evaporate. This attorney is a moron.