BOSTON (WHDH) - Federal investigators arrived in Boston over the weekend to help figure out what caused Friday’s crash on the Green Line.

One trolley crashed into another on the B Line near the Agganis Arena at 6 p.m. Friday, injuring 25 people.

The operator of the first car of the two-car trolley that struck the other trolley from behind has been placed on administrative leave, a spokesperson said. The operator has worked for the MBTA for seven years.

“This should not happen and we will find out why it happened and ensure that it won’t happen again,” MBTA General Manager Steve Poftak said.

People who were on the trolley when the crash happened described the moment of impact.

“All of a sudden it jerked forward really quickly,” Brian Sirman recalled. “People were thrown on the floor. I hit my head a little bit.”

Surveillance video showed one of the trains going by as smoke started to take over.

“Over 30 years of my taking the train you just in general trust that nothing’s going to happen,” Emma Payne said. “It’s going to squeak, it’s going to creek, you might fall onto a stranger, but that’s usually the worst thing that’s going to happen.”

A safety system to help prevent train collisions has been installed on the MBTA’s Blue, Orange, and Red lines, along with the Commuter Rail, but no the Green Line.

That system will start being installed next year and is expected to be online in 2024.

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