This is critical because many domestic violence suspects, based on their agitated emotional state, will make admissible, spontaneous statements that can be used against them later in court. Let them make all the spontaneous statements they want. Furthermore, because the suspect is in a detention status, simply asking general questions like, "Who are you? and "What's Up?" does not constitute interrogation.
If both the victim and suspect are injured, try to determine who the primary aggressor is. Until then, treat both as suspects, keeping in mind the need for medical help if necessary. Document the victim's condition through photographs, diagrams, etc. Remember some injuries may take days to provide visible documentation, so a follow-up may be required in order to file a felony charge.
Take photos of torn clothing, smeared blood or makeup, telephones torn from wall sockets, or any other evidence of the disturbance. Furthermore, if the victim has a restraining order against the suspect, obtain a copy of the order and valid proof that the order has been served.
If the victim does not have a temporary restraining order against the suspect, then information should be given to them to facilitate this.
In San Diego, victims are given a two-page sheet that lists telephone numbers for more than 40 different agencies. The list includes numbers for the SDPD's domestic violence unit, various women's shelters and the city Attorney's Office.