Symptoms Associated With The Five Phases Of Aggression

Most patients with mental health disorders are not aggressive.  However, it is important for nurses to be able to know the signs and symptoms associated with the five phases of aggression, and to appropriately apply nursing interventions to assist in treating aggressive patients.  Please read the case study below and answer the four questions related to it.
Aggression Case Study
Christopher, who is 14 years of age, was recently admitted to the hospital for schizophrenia.  He has a history of aggressive behavior and states that the devil is telling him to kill all adults because they want to hurt him.  Christopher has a history of recidivism and noncompliance with his medications.  One day on the unit, the nurse observes Christopher displaying hypervigilant behaviors, pacing back and forth down the hallway, and speaking to himself under his breath.  As the nurse runs over to Christopher to talk, he sees that his bedroom door is open and runs into his room and shuts the door.  The nurse responds by attempting to open the door, but Christopher keeps pulling the door shut and tells the nurse that if the nurse comes in the room he will choke the nurse.  The nurse responds by calling other staff to assist with the situation.
In-text citations and all references in APA format.

1. What phase of the aggression cycle is Christopher in at the beginning of this scenario?  What phase is he in at the end of the cycle? (State the evidence that supports your answers).
2. What interventions could have implemented to prevent Christopher from escalating at the beginning of the scenario?
3. What interventions should the nurse take to deescalate the situation when Christopher is refusing to open his door?
4. If a restrictive intervention (restraint/seclusion) is used, what are some important steps for the nurse to remember?