He also admitted to investigators that his .40-caliber Smith and Wesson firearm was in his backpack on the trolley, the affidavit said. Authorities said the gun was loaded.

In an MBTA Transit Police affidavit filed in Dorchester District Court, investigators said the driver, Leroy H. Mattison, 42, of Malden, told authorities he reached into his backpack to “take a quick peek” at his phone shortly before the Dec. 29 crash and attempted to delete a posting he had left the night before on the website Reddit.com.

The MBTA driver who crashed his trolley into another train on the Mattapan Line late last year, injuring 17 riders , was using his cellphone during the collision and had brought a gun on board, according to a police report.


MBTA officials on Monday confirmed that Mattison, who was hired in 2001, has been fired.

Transit Police are seeking criminal charges against him, including common carrier’s gross negligence, witness intimidation, and using a mobile phone while operating a public transport vehicle, court records state. A police affidavit says Mattison will be charged at a later date in Malden District Court with improper storage of a firearm.

“The MBTA is extremely disappointed with the alleged conduct of this former trolley operator, who jeopardized the safety of both customers and employees,” the Massachusetts Bay Transportation Authority said in a statement. “The MBTA has strict rules and policies to which all employees must adhere, and will not tolerate conduct that puts passengers at risk.

“Due to these allegations, this individual has been let go and will no longer operate any MBTA vehicles. We are grateful to Transit Police detectives who diligently pursued the facts in this matter and quickly sought criminal complaints against the defendant.”

Mattison declined to comment when reached by phone.

A clerk magistrate hearing is scheduled for Feb. 14 to determine whether the case will go forward.


Train operators are barred from possessing personal cellphones while driving trolleys, and the affidavit said the collision occurred “as a result of operator Leroy Mattison’s attention being distracted by him looking at his personal cell phone, while operating’’ an MBTA trolley.

In 2009, a Green Line crash that injured 49 people and destroyed three trains, caused by a trolley driver who was texting his girlfriend, prompted T officials to implement a zero-tolerance policy on cellphone use.

The MBTA made the rules stricter in 2014, requiring a 30-day suspension for any bus or train operator with a cellphone on the job. That rule change came after a bus crash left an MBTA bus dangling over the Massachusetts Turnpike in Newton. The driver allegedly had a cellphone in her hand. Seven people were injured.

Mattison initially told police he had left his phone inside an inspector’s booth at the MBTA station in Mattapan before the crash, the affidavit said.

But T bus inspector Shirley “Nesse” Slayman told investigators that at some point after the crash, an unknown woman approached her at the station and handed her a backpack, telling her “Someone told me to give this to you,” the filing said.

Slayman opened the bag and recognized Mattison’s cellphone, the document said.

Soon after the woman dropped off the bag, Slayman said, Mattison’s aunt, Celeste Howell, arrived at the station, opened her nephew’s bag, removed his phone, and put it in her own parcel. Howell later gave Mattison his phone at the hospital, records show.


Investigators determined through a forensic search of Mattison’s phone that the device had been used between 11:56 a.m. and 3:10 p.m., including an outgoing call at 2:59 p.m., all after Mattison had started his shift, the filing said.

The search showed phone activity on the Reddit website at 3:10 p.m., around the same time as the crash.

According to court records and officials, two trolley cars traveling inbound collided on a stretch of tracks flanked by the Cedar Grove Cemetery and a river walkway, when Mattison’s train rear-ended the other one.

Passengers described a jolt that tossed riders forward. Officials said the riders who were hurt suffered mostly minor injuries.

The driver of the trolley that Mattison struck had stopped to ask the operators of two trains stalled on the opposite tracks — one was trying to push the other to Mattapan Station after it became disabled — if they needed help.

The operator of the train that had been trying to push the disabled trolley heard a distraught Mattison say after the crash, “I didn’t see him, I didn’t know he was there” and “I’m screwed,” the affidavit said.

Mattison also told a T supervisor that “I tried to help,” the filing said. “I didn’t know, I didn’t hear, they can do whatever they want to me.” He also told the supervisor, “I heard a baby cry.”

He told investigators that after the crash, he gave his backpack to a woman at the scene who appeared “compassionate” and told her to bring it to the inspector’s office at Mattapan Station.


Mattison told detectives he initially thanked Slayman for receiving the bag after the crash, saying to her, “Good looking out, I had my gun in the bag, I could have been [expletive],” the affidavit said.

Slayman chided him for putting her in a bad position, the filing said.

He told authorities he normally leaves his gun in his car, but he couldn’t on the day of the crash because his personal vehicle wasn’t working, according to the filing.

Evan Allen of the Globe staff contributed to this report. Anderson can be reached at travis.andersen@globe.com.