Transit police are seeking this man.


Transit police are searching for a man they say assaulted and threatened an MBTA bus driver during two separate occasions.


MBTA officials have released surveillance images of the suspect, who allegedly spat on the driver of a Route 33 bus on the afternoon of Oct. 21 as it sat at the intersection of River Street and George Street in Boston.


It was not clear what prompted the assault.


Two months later, on Dec. 18, the same man allegedly entered the Route 33 bus as it stopped on River Street in Hyde Park. According to transit police, the driver recognized the passenger as the man who had spat on him.


“When the Bus operator opened the bus doors, the depicted male subject attempted to board the bus. The bus operator, in fear, quickly shut the door as the male subject shouted, ‘When I see you again I’m going to kill you.’”


The suspect is described as a black man between 20 and 25 years old, with sandy brown hair. Anyone with information can contact transit police at 617-222-1050.

The MBTA said it has cracked down on attacks against its employees. The T recently reported that assaults on drivers were down by 32 percent in 2014 compared to 2013. Authorities have credited partnerships with community members and leaders and greater public awareness about the matter.