Lenore's apartment scenes were filmed in Sunnyside, NY. The apartment was converted from a existing dental office. The dentist was paid a hefty price for the use of his office for a one month period. When the filming was over the distraught dentist claimed damages and said it wasn't worth the price to close his practice for the filming.
Emily Lloyd complained for years that she had been treated very badly by Peter Falk during the filming of this movie, even claiming that he had once become so angry with her that he slapped her face in front of the whole crew.
At one point, Falk's character is called "Dapper Dino". This is a reference to John Gotti, aka the "Dapper Don", who was head of the Gambino crime family in New York City at the time of this film.
The car explosion scene was filmed on Renfrew Avenue in Elmont, New York adjacent to Elmont Junior High School. Curious students lined the area and were held back by crew and security as Brenda Vaccaro signed autographs to the masses.
This movie was filmed in multiple locations. Atlantic City, NJ, Long Island City, Sunnyside and Elmont, NY.