By Kristin LaFratta, MassLive

A second investigation has been opened into the Massachusetts State Police trooper who shot an ATV driver during a police confrontation on Interstate 93 over the weekend after a report tied him to a stream of racist online messages.

Under the username "Big Irish," Trooper Matthew Sheehan has a more than five-year history of posting angry, racist messages on a forum for Massachusetts police officers, the Boston Globe reported, citing corroborating details and two unnamed sources.

Sheehan shot Aderito Monteiro, 28, of Randolph, in the foot last Saturday after Monteiro allegedly drove his ATV toward police on Route 93. Monteiro was one of more than 25 people riding motorcycles and ATVs down Route 93 in Boston. State police arrested seven people while most others dumped their bikes and escaped by foot.

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A report by the Boston Globe found Mass. State Trooper Matthew Sheehan was the man behind the "MassCops" online account "Big Irish."

A long history of messages on the "MassCops" website reveals a person full of hate toward minorities. The user refers to people in particular neighborhoods, including Dorchester, as "scumbags."

On a forum about an officer-involved shooting in Worcester in July 2012, "Big Irish" wrote, "Note to [expletive] scumbags!!!! 'You try and run us over and you will die!!!! Good shoot ALL DAY LONG!!!!!!!"

The user posted several messages of respect for fallen officers. He also shared identifying information, including his hometown, age and information on his 12 years in the department.

Massachusetts State Police have opened an internal affairs investigation into the actions of Matthew Sheehan, according to spokesman David Procopio. Sheehan is on standard administrative leave after shooting Monteiro on Saturday, though a hearing will be held on Friday to determine Sheehan's duty status during the investigation.

"The tone and nature of these posts are repugnant and clearly do not reflect the values, ideals and opinions of the Massachusetts State Police," Procopio told MassLive.

Sheehan faces the possibility of suspension without pay during the investigation, Procopio added. All job-issued equipment, including Sheehan's cruiser and use-of-force equipment have been seized by state police.

The Boston Globe report found Sheehan was the subject of five internal affairs complaints in the last seven years. In 2016, it is reported Sheehan earned $233,351 as a state trooper.

Below are several posts shared by "Big Irish" on MassCops.com. Some contain graphic language.

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A 2012 post about a Worcester man fatally shot by an officer.

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A 2016 post about Dorchester. This comment was made about a news story that reported a group of teenagers had allegedly attacked a postal worker.

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A 2016 post about handing jurisdiction of Boston’s Seaport from Massachusetts State Police to Boston police.

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A 2017 post about a Lawrence officer who was placed under investigation after a traffic stop was recorded.

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A 2016 post about a remembrance for those killed in the Sept. 11 attacks. The posts show a reverence for the uniform and fallen officers.

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A 2015 post about a physical altercation between an MBTA officer and woman.

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A 2015 post about an active shooter reported on the MIT campus.

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A 2015 post about Boston police shooting a suspect in a CVS parking lot.

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A 2013 post about a rowdy event in North Carolina in which beer was thrown at police.