The district attorney’s office will investigate whether this merits criminal prosecution, the release said.

MBTA spokesperson Joe Pesaturo said in a statement that the agency’s top priority is the safety of its customers and employees.

“The MBTA has been cooperating with the District Attorney’s Office since the summer, and the T will continue to do so,” the statement said. “Following September’s preliminary findings by the National Transportation Safety Board, the MBTA acted swiftly to address the conduct of the train operator, who was responsible for the collision.

“The MBTA will continue to emphasize safety in its employee training programs, and the T will hold any employees accountable for actions that adversely impact service or customer safety.”

The governor’s office did not respond to a request for comment.

Since the Green Line crash in July, Rollins noted, the MBTA was connected to three other major safety incidents. In September, Boston University professor David Jones fell to his death through a rusted, closed-off staircase near the JFK/UMass MBTA Station in Dorchester. Two weeks later, an ascending escalator at the Back Bay Station suddenly reversed, causing a bloody pileup of people that sent nine to the hospital. Later that month, a Red Line car derailed at the Broadway Station, upending commutes.

“This list of failures and tragedies appropriately makes the T-riding public and all of us question the value the MBTA is placing on safety,” Rollins said in the statement. “State agencies are accountable to the public they serve. And this two-month period shows that we deserve better from the MBTA. When their acts and omissions put the safety of community members and their own employees at risk, sometimes the only means of driving change is through the courts, and public demands for action. That is why we make this formal announcement today.”

The full scope of the DA’s investigation was not clear Thursday evening. The DA is responsible for crimes that happen in the county, while the MBTA’s operations span far outside Suffolk County.

The Green line driver blamed for the July crash by prosecutors, Owen Turner, has been charged criminally, pleading not guilty in October to counts of gross negligence of a person in control of a train and gross negligence of a person having care of a common carrier.

The case remains pending.

In announcing the separate probe Thursday into the MBTA itself, Rollins’s office said that under state law, to prove corporate liability, prosecutors must show a person committed a crime as the government alleges Turner did, that the defendant was involved in the business (in this case, the T) to be charged, and that the suspect was vested with authority to act on the agency’s behalf.

“Mr. Turner was operating at three times the speed limit at the time of the crash,” Rollins said. “As his colleagues and supervisors were aware, he had a reputation for speeding and a history of violations.”

Rollins added that the T “had a duty” to address Turner’s allegedly reckless behavior.

Citing court records, the Globe reported in September that Turner had a history of speed infractions at the T and said he could not remember what caused the crash.

Investigators said in the report that Turner had been “suspended on six different occasions for a total of one hundred and fifty-seven days, to include being issued a ten-day suspension/Final Warning on July 2, 2016, for ‘speeding’ while operating a Green Line trolley.”

The report cited three instances in 2020 in which he allegedly operated Green Line trolleys above the speed limit, including an April 10, 2020, instance in which he was allegedly traveling 43 miles per hour in a 25 miles per hour zone.

Court records show Turner told police that after receiving a white signal light indicating he was cleared to proceed to the next stop, “he does not remember anything” before his trolley rammed into the one in front of it. Trolley operators are supposed to maintain a 500-foot distance between each other while in motion on the Green Line, according to the court records.

The additional investigation into the MBTA by prosecutors signals a shift toward looking at systemic causes of the crash instead of faulting only the driver, observers said.

“The system had to fail at multiple levels for this to happen,” said Stacy Thompson, executive director of LivableStreets Alliance. “It is frustrating that perhaps the only mechanism we have to deal with chronic lack of oversight is the DA taking this step . . . People cannot be getting hurt on our systems anymore.”

In the stretches of Green Line track that mix with car traffic, like the stretch where the July accident happened, the trains are wholly dependent on their operators to avoid collisions.

The National Transportation Safety Board first recommended the MBTA install a train collision prevention system called positive train control in 2009 following a Green Line train collision that year that injured 49 people and another one in 2008 that killed a train operator. The system is able to apply brakes as one train approaches another, even if an operator doesn’t.

In 2019, 10 years after the NTSB’s recommendation, the MBTA awarded a contract for an alternative, less expensive safety system that it says will accomplish the same benefits. It won’t be fully implemented until 2024.

In October, following the recent series of safety incidents, MBTA general manager Steve Poftak said he was going to hold a meeting to determine if the agency can speed up the implementation process.

On Thursday, Pesaturo said, “The MBTA continues to explore opportunities to accelerate the ongoing work.”