The Special Investigations Unit was called in after a 29-year-old man was shot by police at a hospital in Fort Erie.
It happened around 7:50 p.m. last night at the urgent care centre at the Douglas Memorial Site after reports of a stabbing.
When police arrived, the SIU says they found a 61-year-old man with stab wounds.
There was an "interaction between the officers and the 29-year-old man" who was shot by police.
Both of the injured men were taken to Erie County Medical Centre in Buffalo for treatment.
The urgent care centre in Fort Erie is closed until further notice. Patients are being redirected to the Niagara Falls hospital.
The SIU has assigned five investigators and three forensic investigators to the incident.
Anyone with information or who witnessed the incidents is asked to contact the SIU.