Tulsa Gunman Bought Rifle Hours Before Mass Shooting; Targeted Doctor Over Post-Surgery Pain: Cops

Tulsa, Oklahoma -- A gunman who killed four people at an Oklahoma medical building Wednesday reportedly bought an AR-15 style rifle just hours before the shooting. He targeted his former doctor, blaming him for his continuing pain after surgery, police said.

The suspect, identified as Michael Louis, bought a semi-automatic handgun from a local pawn shop on May 29 and a rifle at 2 p.m. Wednesday. He went inside the orthopedic office at Saint Francis Health System in Tulsa at around 5 p.m. Wednesday.

Louis then opened fire, killing his former doctor, Dr. Preston Phillips, and three others, including Dr. Stephanie Husen, receptionist Amanda Glenn and a patient, identified as William Love, officials said at a press conference Thursday. The 45-year-old shooter from Muskogee took his own life after the rampage, NBC News reported.

Louis underwent back surgery under Dr.Phillips on May 19 and was released after the treatment on May 24. However, he complained of continuing pain after the surgery and received additional treatment at the hospital Tuesday. According to reports, Louis called the doctor's office again Wednesday asking for additional help, although it was unclear what sort of help he was seeking, the NY Post reported.

Officials have recovered a letter from Louis "which made it clear that he came in with the intent to kill Dr. Phillips and anyone who got in his way," Tulsa Police Chief Wendell Franklin told reporters. "He blamed Dr. Phillips for the ongoing pain following the surgery."

Dr. Phillips was a board-certified orthopedic surgeon who specialized in spinal surgery and joint reconstruction, according to the website of the medical facility.

While sharing her condolences, Vice President Kamala Harris called for the need to pass "common-sense gun safety laws." "All of us hold the people of Tulsa in our hearts, but we also reaffirm our commitment to passing common-sense gun safety laws...No more excuses. Thoughts and prayers are important, but not enough. We need Congress to act," she said Thursday.

Tulsa shooting is the 233rd mass shooting in the U.S. this year. The tragic incident happened just a week after the mass shooting at Robb Elementary School in Uvalde, Texas, that killed 19 students and two teachers.