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In December, 17 people were injured after a trolley car collided with another in Boston, which was initially attributed to an “operator error.” But more details have now emerged, with authorities saying the trolley driver was trying to delete a Reddit post right before the crash. Police say the driver, 42-year-old Leroy H. Mattison, also had a loaded .40-caliber gun in his backpack. Mattison has since been fired.

According to an MBTA Transit Police affidavit obtained by The Boston Globe, Mattison admitted that he was trying to delete a Reddit post he had submitted the previous evening. Authorities say Mattison told them he was trying to retrieve his phone from his backpack to “take a quick peek” before the crash. According to police, Mattison’s phone activity showed that someone was on Reddit around the time of the collision. There was also reportedly an outgoing call made from Mattison’s phone about ten minutes before the crash.

Aside from the fact that surfing Reddit while operating heavy machinery is stupid dangerous, it’s also against MBTA rules. “Any employee found to have possession of or using a prohibited electronic device will be in violation of this Special Order,” an MBTA policy implemented in 2014 states, WBUR News reports. “This will result in a 30 day suspension with recommendation for discharge for the first offense; this is regardless of your prior record or work history.”

Mattison first told authorities that he had left his phone in a booth at the trolley station, but bus inspector Shirley Slayman was handed a backpack that included Mattison’s phone. “Someone told me to give this to you,” the woman who handed Slayman the bag said.

The affidavit states Mattison later admitted that he had given his backpack to a woman after the crash and asked her to bring it to the station inspector. “Good looking out, I had my gun in the bag, I could have been [expletive],” Mattinson says he told Slayman, according to police.