The name of the manor house where Miss Jane Marple conducts her inquiries is called Rutherford Hall in Dame Agatha Christie's novel. This was changed to Ackenthorpe in this movie to avoid comparison with the surname of Dame Margaret Rutherford (Miss Jane Marple).
The character of Miss Jane Marple's librarian friend, Jim Stringer, was not part of the original story (and never featured in any of the Christie books). The part was written for Stringer Davis, who was married to Dame Margaret Rutherford.
Despite privately remaining unimpressed by the film, Agatha Christie dedicated her 1962 novel "The Mirror Crack'd From Side to Side" to Margaret Rutherford "in admiration".
This movie was a success at the box-office, earning MGM a profit of $342,000 ($3.29M in 2022) according to studio records. Rather more remarkably, it was the studio's biggest success in what was a very lackluster year, financially.
The part of Alexander was dubbed by Olive Gregg, who also dubbed the voice of David in Village of the Damned (1960).