Norbert Berthiaume —MBTA Transit Police

A Medford man was “caught in the act,” MBTA transit police say, after an officer saw him allegedly trying to steal a bicycle locked up at Oak Grove station Monday afternoon.

At 4:21 p.m., an officer on patrol saw Norbert Berthiaume, 28, trying to remove a bicycle from a rack using a sheet metal shear, authorities said in a statement.

“The officer immediately proceeded in his direction, upon seeing the officer Bethiaume fled,” officials said. “The officer gave chase and with the assistance of a Good Samaritan was able to apprehend and place Bethiaume into custody.”

According to officials, during the booking process, police learned there were also several arrest warrants for Bethiaume from East Brookfield District court for operating under the influence of drugs; possession of Class A drugs; possession of Class B drugs; and, from Boston Municipal Court, a warrant for possession of Class B drugs.