[Update: 2:10 p.m.] An email from MBTA spokesman Joe Pesaturo, Boston.com reports, said human error caused Monday’s Green Line derailment.

The driver of the Green Line trolley that derailed west of Kenmore Station on Monday was fired by the MBTA in 2010, and later rehired, after a union filed a grievance challenging the decision.

Sydley Gardner, 48, CBS Boston reports, was fired in 2010 for failing to report an accident involving a then-Boston University student. Gardner was driving a Green Line trolley along Commonwealth Avenue when it struck BU student Annie Wong.

Wong, CBS Boston reports, was standing behind the yellow line at a station platform when she dropped money on the ground. “My reflex was to bend over and pick it up, and then I blacked out,” she told WBZ-TV.

The train, she said, struck her in the head. When she woke up, Gardner was trying to help. According to the report, Gardner helped Wong onto the train and traveled a few stops down the line, where police eventually arrived to ask questions about the incident.

Gardner wasn’t found responsible, but sources tell CBS Boston that he never filed a “necessary” report, an action which eventually led to his dismissal.

BostInno reached out to MassDOT, which wasn’t able to provide additional comment on the incident.

In 2011, Boston Carmen’s Union filed the grievance against Gardner’s firing, a source close to the situation told BostInno. Gardner was reinstated in 2012.

On Monday, Gardner’s train derailed, colliding with a tunnel wall, near where D and C branch tracks intersect. Ten people were hurt, nine of which had to be taken to local hospitals. According to the MBTA, no track or signal problems were found.

Now, the focus is on Gardner, after the T confirmed the trolley’s speed at the time likely contributed to the accident.

Gardner was hired by the T in 2008. Although he had a history of driving violations, state law didn’t require the T to check his records.