The director is a former cop from the crime department. Once as a young cop, he have to investigate a murder leaving a young girl orphan. This case hits him a lot. In 2002, he meets again with the orphan who was now a young mother. He so decided to do the movie and invite her during the filming that was quite both hard and relieving for both of them. In fact, the film's prologue seems to reflect this: "The story is based on a case that caused me indescribable pain for many years."
The french title come from one of the weapon used in the movie, the MR73, a pistol manufactured by Manurhin in 1973 (hence the name).
This one fired .357 or .38 ammunition and had a reputation of solidity and accuracy.