When in the GCPD, Batman can view the Evidence Locker, which contains weapons an gear confiscated by villains throughout Batman's adventures in Arkham Origins (note elsewhere also the references to the Blackgate Riots that took place during that game), Arkham Asylum, and Arkham City - all of which have voice recordings from Aaron Cash. You can find Talia's sword in the Evidence Locker, and inspecting it will cause Batman to have a private moment of reflection. Any additional enemies apprehended during the course of Arkham Knight will see their weapons and items added to the Evidence Locker.