Domestic Disturbance

PC Recowski has responded to a domestic disturbance. Upon arrival, he rings the doorbell and observes a male peeking out from the living room holding what appears to be a large knife.  Police dispatch advises that the man’s partner is still in the residence, hiding in the closet where she is making the phone call from.  She is terrified and fears for her life. She did not tell 911 about the knife.  Explain in detail what steps PC Recowski could take at this point to secure the scene and to arrest the suspect.   Explain all authorities and powers at the disposal of the police officer and identify any potential charges that he could lay and how these charges would be submitted.