This comment applies only to the guilt phase of the trial.

By using the PTSD argument in this phase, you might have to say that the PTSD caused him to do the act (in effect, admitting the crime).

So, you run the risk of doing to your client what Mike Tyson's lawyer did to him. Paraphrasing the argument as I recall it - His childhood and life were so traumatic it turned him into an animal, just an animal.

A jury might well symphathize with a vet, but it is not likely to symphathize with an animalistic murderer, rapist or home invader.

Now, PTSD might work in a case that has some other redeeming factors, such as Anatomy of a Murder where temporary loss of mental capacity was allowed as a defense (with PTSD claimed as a basis for that). Or, in the Astan HT case, where premeditated murder ended up as a manslaughter plea - and the judge gave a light sentence.

In most jurisdictions in non-death cases, the jury decides guilt and the judge sets sentence. So, the PTSD evidence would most likely be heard by the judge if not introduced in the guilt phase.

Situational awareness needed on the part of the lawyer - plus good luck of the draw as to judge and jury.