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Troubling details have emerged about the Kentucky doctor who was dragged off a United Airlines flight at O'Hare International Airport on Monday.

Dr. David Dao was charged with 98 felony drug counts in 2003 for illegally prescribing and trafficking painkillers such as hydrocodone, OxyContin and Percocet, according to TMZ.

According to a criminal complaint filed against him, Dao also allegedly solicited sex from a male patient in exchange for drug prescriptions.

Dao, who attended medical school in Vietnam in the 1970s, was eventually convicted on six felony counts of obtaining drugs by fraud and deceit.

Dao was placed on five years of supervised probation in January 2005, although he surrendered his medical license one month later, according to the Courier-Journal.

The Kentucky Board of Medical Licensure allowed Dao to resume his practice in 2015, but only under certain conditions.

See people on social media react to United Airlines kicking Dao off his flight:

12 PHOTOS People react to United Airlines kicking a passenger off a flight See Gallery People react to United Airlines kicking a passenger off a flight Pepsi: We are the most hated company right now. 😓 United Airlines: 1 sec - Hold my Pepsi. #PEPSI #unitedAIRLINES Not so friendly skies huh @united ? Makes me sick now how you treat customers. I hope he sues hard. #unitedairlines https://t.co/D13SDvHfLq You want passengers to give up their seats because you have piss poor planning & then beat them up? Shame on you. @united #unitedAIRLINES Apparently @united 's inability to coordinate a flight makes violent assault against customers ok. Never flying #UnitedAirlines again NEVER flying @united ever again! Horrific, brutal, intolerable treatment of passenger, + tone-deaf "apology" from CEO. #UnitedAirlines Dear United Airlines: People have smart phones. Perhaps @MerriamWebster can help #United Airlines with the definition of "volunteer" United Airlines to United Airlines: "I see your legging-gate, and I raise you a passenger beating" #UnitedAirlines #United #flight3411 Look on the bright side, United Airlines. After this incident, you'll never have to worry about a flight being overbooked again. You thought United Airlines was tough on folks who wear leggings. Just wait to see what they do to folks in sweat p… https://t.co/x5Nzp7gcn1 Poor planning on your part doesn't constitute an emergency on ours. Fly Southwest. Fly Delta. Hell, fly Spirit. Not #UnitedAirlines Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

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