June 1, 2011— -- Orlando police are probing a stunning murder-suicide after a surgeon was shot dead in a Florida hospital parking lot by one of his organ transplant patients.

Dr. Dmitry Nikitin was shot dead outside the Florida Hospital in Orlando Thursday afternoon by 53-year-old Nelson Flecha, who then walked to another level of the parking structure and turned the gun on himself, police said.

Flecha approached Nikitin, 41, as the doctor left the hospital after just finishing his shift. As he walked towards his car he was confronted by his former patient, who received a liver-kidney transplant performed by Nikitin a year ago at the same hospital.

The two men reportedly talked briefly before Flecha pulled a gun and killed the surgeon, firing several rounds. Shortly thereafter he took his own life.

Multiple weapons were reportedly found of the scene, and Lt. Barbara Jones of the Orlando Police Department told Reuters that video from cameras at the garage confirmed the theory that the tragedy was a murder-suicide.

"There is no rational reason to cold-bloodedly kill another human being," Jones said.

Authorities haven't released the video footage.

The Russian-born doctor immigrated to the United States in 1996, seeking a better life for himself and his family. He was a husband and father of four children -- his youngest son just 3 years old.

An organ transplant specialist, Nikitin successfully performed the transplant on Flecha, Nevertheless, neighbors say that Flecha remained an angry and bitter man.

Neighbors of Flecha who spoke with ABC News Orlando affiliate WFTV said that he was active and moving around, with no visible side effects from the surgery, but they also say he was still grumpy and angry.

Flecha, who had no prior criminal history, was also listed as a missing person out of Bronx, N.Y., but he's been living in Florida since 2010, according to WFTV.

Investigators say that they might have to subpoena Flecha's medical records to get a better sense of his motive and why this tragedy took place.

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