Would the NYC Transit Police actually be knocking on suspects doors and investigating a high profile crime like this? Wouldn't a higher arm of law enforcement be involved in a case like public transportation hijacking? The FBI possibly?
Technically, the passengers, conductor and motorman were kidnapped, I guess, but the crime never crossed state lines. I don't know what F.B.I. jurisdiction was back then. Of course, we only see Garber and Petrone investigating. Maybe there were other folks interviewing the passengers, tracking down Mr. Blue's record, etc. It was a pre-Internet age, so data was on paper or in people's heads. "May I bone your kipper, Mademoiselle?"
As this is a pre-9/11 movie made in the early '70's, the New York City Transit Police was a vital, active Police agency in NYC. As the crime occurred on Transit System property, they would be the lead agency in the investigation. Acts of terrorism in the Big Apple, like the first World Trade Center bombing in the 1990's and the destruction of the World Trade Center in 2001, were years away. New York City in the 70's had three major police agencies: NYPD, NY Transit Police and the New York City Housing Authority Police. The latter two were absorbed into the NYPD sometime later. The previous posters comments about the FBI's lack of Jurisdiction due to the failure of crossing any state lines, is true as is the statement that other agencies, like NYPD and other Transit Police detectives, would be investigating other aspects of the crime and the suspects We only see Lt. Garber and Lt. Patrone investigating former subway motormen, as they should be doing.