ABC News June 2, 2022

Tulsa mass shooter allegedly gunned down his doctor after asking for help with pain

WATCH: Police give possible motive in Tulsa shooting

A patient gunned down his surgeon and three other people in a mass shooting at a Tulsa, Oklahoma, medical building on Wednesday after blaming the doctor for his pain, according to police.

On May 19, the suspected gunman underwent back surgery. Dr. Preston Phillips -- one of the four people killed in the shooting at the Natalie Building, a five-story medical complex at Saint Francis Hospital -- was the suspect's doctor in that surgery, Tulsa Police Chief Wendell Franklin said at a news conference Thursday.

MORE: Timeline: How the Tulsa medical office mass shooting unfolded

A letter recovered on the suspect, Michael Louis, made it clear "that he came with the intent to kill Dr. Phillips and anyone who got in his way," Franklin said. "He blamed Dr. Phillips for the ongoing pain following the surgery."

St. Francis Health System
Dr. Preston J. Phillips, one of the victims in the June 1st shootings by alleged gunman Michael Louis at the Natalie Building at Saint Francis Hospital, Tulsa, Okla., is seen in an official staff portrait.

Louis bought an AR-style semi-automatic rifle just hours before the shooting, Franklin said. He bought a 40-caliber pistol from a pawn shop on May 29, police said. Both appeared to be legally purchased, police said.

The three others killed were Dr. Stephanie Husen, office employee Amanda Glenn and patient William Love, Franklin said.

St. Francis Health System
Dr. Stephanie J. Husen, one of the victims in the June 1st shootings by alleged gunman Michael Louis at the Natalie Building at Saint Francis Hospital, Tulsa, Okla., is seen in an official staff portrait.

"They stood in the way" so the suspect "gunned them down," Franklin said.

MORE: What we know about the Tulsa mass shooting victims

Louis' body was found in the lobby area of Phillips' office from an apparent self-inflicted gunshot wound, police said.

J Pat Carter/Getty Images
Police respond to the scene of a mass shooting on at St. Francis Hospital on June 1, 2022 in Tulsa, Okla.

Authorities said Louis had been released from the hospital on May 24, five days after his surgery. After his release, Louis called Phillips several times over several days complaining of pain and wanting additional treatment, the chief said.

On Tuesday, Phillips saw the suspect again for additional treatment, the chief said. On Wednesday, the suspect called the doctor complaining of back pain and wanting additional help, the chief said.

MORE: Here's what states are doing to address gun control

At 4:52 p.m. local time Wednesday, a patient on a video call with a doctor called 911 after the doctor told her there was shooting, police said. The first 911 call came in at 4:53 p.m. and police arrived at 4:56 p.m., the chief said.

A gunshot heard at 4:58 p.m. was believed to be the suspect's self-inflicted gunshot wound, police said.

Phillips was found dead in an exam room, police said.

MORE: Biden to deliver prime-time address on guns

As police continued searching the hospital, they said they found a woman hiding under a desk near the suspect's body. The woman said she was unharmed but saw the suspect shoot himself, police said.

Several victims were treated at hospitals for gunshot wounds and later released, officials said.

There's no evidence that Phillips had any concerns about Louis, hospital officials said.

Muskogee County Sheriff’s Office
Michael Louis, the alleged gunman in the June 1st shooting of multiple people at the Natalie Building at Saint Francis Hospital, Tulsa, Okla., is pictured in a 2017 arrest photo released by released by the Muskogee County Sheriff’s Office.

Thirty minutes after the shooting, authorities received a call from a woman who said her husband killed multiple people at Dr. Phillips' office, police said. Louis allegedly contacted his wife before or during the shooting "to let her know what he had done," the chief said.

MORE: 'Feckless' ammunition laws under scrutiny following Uvalde, other mass shootings

The chief called this latest mass shooting a "senseless tragedy."

"This is yet another act of violence upon an American city," Franklin said. "We train for instances such as this. And I'm overwhelmed and proud of the men and women, all those that responded."

"Our training led us to take immediate action without hesitation," Franklin said.

Tulsa Police Dept.
Tulsa Police department attend the scene of a shooting in Tulsa, Okla., June 1, 2022.

Tulsa Mayor G.T. Bynum told reporters, "I spoke with an officer yesterday who is a seasoned veteran of the department. And he was one of the first people to get here. And he said, 'Mayor, it was like the beaches of Normandy out there. Everywhere I looked, to my left and my right, there were officers running towards that building, jumping over bushes, getting around anything in their way between them and that threat so that they could save people.'"

Dr. Ryan Elizabeth Parker, associate chief medical officer at St. Francis, said at Thursday's news conference, "We were just starting to process the grief and emotions that being on the front line of a pandemic had left with us, and now this tragedy. ... Our job is to help and heal, and we are here to do our job, even if it's with broken hearts."

Nathan J. Fish/The Oklahoman /USA Today Network
Medical personnel look on as Tulsa Police Chief Wendell Franklin speaks during during a press conference, June 2, 2022, in Tulsa, Okla, outlining the timeline of events of a mass shooting that killed multiple people at Saint Francis Hospital on Wednesday.
J Pat Carter/Getty Images
Associate Chief Medical Officer Ryan Parker and Saint Francis Hospital CEO Cliff Robertson react during a press conference at Saint Francis Hospital on June 2, 2022 in Tulsa, Okla.

In the wake of the Tulsa shooting, Vice President Kamala Harris again urged Congress to pass gun safety laws.

"No more excuses. Thoughts and prayers are important, but not enough. We need Congress to act," she said Thursday.

ABC News' Jenna Harrison Esseling, Justin Ryan Gomez and Matt Fuhrman contributed to this report.