The T.P.F. Insignia on Garrett Morris' collar is for "Tactical Patrol Force", an N.Y.P.D. unit formed in 1959.
One of the burglars looks into a sack taken out of the safe and exclaims in delight, "Double eagles!" The double eagle is a $20 gold coin, no longer made. One of them is now worth several thousand dollars.
The apartment building in the movie is in reality the Convent of the Sacred Heart, whose address is indeed the one given as that of the building, 1 East 91st Street.
Sidney Lumet says in his book that there was a problem during exterior shooting in New York. The funeral of a notorious mafia kingpin was taking place while they were filming, and bystanders among the attendees asked for a copy of the film, because they were unhappy at the possibility that their faces might show up on film.