Oklahoma Gunman Targeted Doctor With Assault Rifle He Bought That Day

However, Louis returned to the Oklahoma hospital on May 31, claiming he was suffering from immense back pain, only to return the following day when the attack unfolded.

Louis succeeded in killing Dr Phillips.

According to Franklin, the suspect 'came in with the intent to kill Dr Phillips and anyone who came in his way'.

He said a letter was found on Louis confirming the shooting was a targeted attack. 

"They stood in the way and (the suspect) gunned them down," Franklin said.

Franklin also revealed that police arrived on the scene within three minutes of receiving a call informing them was an active shooter in the building.

"When we get that call, we are going to disregard any safety measures that we might have for ourselves and we are going to go in the building to deal with the threat," he said.

"Our philosophy is that we will stop the threat and we will do that by any means necessary. That’s how we train."

Franklin applauded law enforcement, the FBI, the United States Marshals Service, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and community members, saying they had acted 'heroically' during the incident.

Receptionist and mother-of-two Amanda Glenn and Dr Stephanie Husen, an orthopaedic surgeon specialising in sports medicine, were also killed.

Following the mass shooting, Chief executive of the Federation of American Hospitals Chip Kahn said: "Enough is enough. This must stop. Hospitals are pillars of our communities."