"Mental Health in ED"

I attended the local ED with a patient who was brought in by paramedics in an ambulance post self-harm/suicide attempt. Patient had superficial lacerations to their arm and had been exposed to gas. The patient was discharged after approx. 2.5-3 hours without even seeing a mental health clinician - even after I explained to the treating doctor that the patient had ongoing Suicidal ideation and thoughts of harm to self. The patient told me, and their partner who was not in ED, that if they were let out of ED that they would go home and kill them-self. 

There was no trust in the people who brought the patient in. Police were let leave before the patient had even woken up and the staff, in my opinion, were not listening to what was important. This patient had presented to ED approx. 7-10 days prior for the same issues and was discharged with minimal follow up then also. 

How is one supposed to help those who don't have the capacity to make these decisions, when the very people who are supposed to provide this assistance are refusing to listen to the people around them?

A patient who doesn't want help in that moment, who knows the right things to say, will say anything to be allowed to go home. 

I believe there was no risk assessment completed, at the very least. In my opinion, not an accurate one based on the information being given. The treating team was told that the patient would be going home alone to where these injuries occurred and allowed the patient to walk out without formal assessment after being brought in under section 351.