Dylann Roof, the alleged racist mass murderer who killed nine people at the Mother Emanuel church in Charleston, S.C., had been charged with illegal possession of Suboxone last year, CBS News reports. Some addiction experts say this should have been a red flag that the 21-year-old was “troubled.”

Suboxone is the brand name for a medication used to treat people who are dependent on opioids, like heroin or prescription painkillers. Last February, Roof was found to be carrying a pack of Suboxone strips without a prescription, when he was arrested for trespassing at a South Carolina mall. He was charged for felony possession in addition to trespassing.

Roof’s mental health and sobriety have been questioned by the media. But addiction experts say use of Suboxone alone would not contribute to his violent act.

"There is no specific research showing that this specific medication has been linked to aggression,” said Dr. Adam Bisaga, CUMC psychiatry professor and researcher at New York State Psychiatric Institute. “In fact, when used properly this medication would stabilize people who otherwise would be irritable, such as heroin addicts undergoing withdrawal and feeling anxious and irritable."

Doctors say Suboxone, which is similar to heroin and prescription painkiller OxyContin, is a safer alternative that has been successful in treating opioid dependence and withdrawal. However, the drug is highly-addictive. In recent years, it has become increasingly available on the black market, as people distribute their prescriptions via illegal channels.

But though the drug itself is unlikely to cause violent behavior, Roof’s illegal possession of the drug should have been a warning sign that he is “troubled,” according to a representative from a South Carolina luxury rehab.

“The fact that he participates in illegal activities such as using prescription drugs not prescribed to him shows that he's troubled,” said a medical associate from Drug and Alcohol Rehab Charlotte. “People who use Suboxone recreationally are more susceptible to participate in other crimes, such as murdering people in a church.”

The representative went so far as to suggest that if Roof had faced harsher consequences for Suboxone possession, his killing spree could have been avoided.