Joseph Michael Swango, MD born in Tacoma, Washington is a former medical doctor turned serial killer who murdered dozens of his patients over the course of two decades in Zimbabwe, Illinois, Ohio, South Dakota and New York.
In 1983, Swango worked in Rhodes Hall at Ohio State University healthy patients were dying mysteriously on floors where Swango was an intern. One nurse caught Swango injecting an unknown medicine into a patient. The nurses concerns were brushed off by administrators as them being overly paranoid.  Still, OSU pulled his residency offer when his internship ended.
In 1984, Swango began working in Quincy, Illinois and it didn't take long for paramedics and staff to notice that whenever Swango made coffee or brought in food that many of them became ill. Swango was arrested and found to be in possession of arsenic and other poisons. He was arrested, charged, convicted and given a 5 year prison sentence for poisoning his co-workers. His conviction set off the alarms back at OSU and a decade later admitted that they should have called for an outside investigation.
In 1991, Swango legally changed his name to Daniel J. Adams and in 1992 he began applying for residency and forging documents to reestablish himself as a physician and landed a job at Sanford USD Medical Center in Sioux Falls, South Dakota. Swango attempted to join the American Medical Association who discovered his poisoning conviction.  He fled the country in 1994 and went to Zimbabwe using forged documents to get work at a hospital, patients began dying mysteriously and Swango was suspended. 
In 1997, Swango was arrested at a Chicago airport on a layover attempting to go to Saudi Arabia.
The FBI believes that Swango is responsible for approximately 60 deaths.

One page handwritten letter dated Thu 31 Jan signed, Mike.

Michael Swango MD Signed Prison Letter