A lawyer friend of mine asked the FCPD several times before finally getting an answer on the ammunition:
http://le.atk.com/general/federalproducts/pistol/tacticalhst.aspx
I believe he said they all carried .40 S&W, but I know that they use Federal HST (at least they did when he asked). He asked for the same reason as the OP, to minimize any potential legal troubles.
I highly recommend this course for anyone who thinks he may have to defend himself in Virginia one day That means everyone I guess :P
http://defensiveforce.com/?page_id=7
Before attending, I had already taken the NRA course to obtain a Virginia Concealed Handgun Permit, several subsequent self defense courses, and I read extensively through Virginia and Federal firearms laws. I still found that I had many misconceptions about the legal bounds of self defense. This is a tricky and misunderstood portion of law. Since we all may need to defend ourselves one day, I think it's imperative that we learn the particulars that only a legal expert on the subject can teach us.
The class is instructed by Dave Rittgers who is a member of the Virginia bar. He is currently a legal policy analyst who concentrates on civil liberties, counterterrorism, and criminal justice at the Cato Institute. Prior to joining Cato, he served in the United States Army as an Infantry and Special Forces officer (Captain), including three tours in Afghanistan. He continues to serve as a reserve Judge Advocate.