The investigation into the deadly crash of the Mexican navy’s tall ship into the Brooklyn Bridge is focusing on the ship’s engine as well as a tugboat that was pulling the vessel through the East River.

In a scene captured in multiple videos, the training vessel, called the Cuauhtemoc, could be seen traveling swiftly in reverse upriver toward the bridge near the Brooklyn side of the East River. Then, its three masts struck the bridge’s span and snapped, one by one, as the ship kept moving.

The lead investigator into the incident, Brian Young with the National Transportation Safety Board, says the main focus is on the engine.

“We will look at the status of the engine, we will look for any failures, we will look for engine inspections, and we’ll talk to the crew on what may have possibly happened with the engine,” he said during a preliminary briefing.

The Cuauhtemoc was backing out of Pier 17 near the Brooklyn Bridge along with a tugboat on Saturday night to head south toward New York Harbor before setting sail to its next destination in Iceland. As the ship cleared the dock and pivoted it continued to move in reverse, rapidly approaching the bridge before its three 147-foot masts hit the underside of the 142-year-old span, causing them to partially collapse. The crash left two crew members, a cadet and a sailor, dead and another 27 injured, including two who are in critical condition.

Investigators are also looking into what role the tugboat may have played in the incident.

Videos posted online show the tugboat pushing against the bow of the ship but then rushing toward the stern in an attempt to stop it from crashing.

“Without the engine failure, the ship would have maybe drifted into the bridge, but it wouldn’t have hit it at speed,” a maritime historian at Campbell University, Salvatore R. Mercogliano, said to Reuters.

“The engine failure drove the ship into the bridge. And it’s not exactly clear what role the tug could have done to prevent that from happening,” he said.