Why did bank robbers begin forcing cashiers to give up safe keys and combinations in the 1870s?

In the 1870s, bank robbers began forcing cashiers to surrender safe keys and combinations because the locks and safes of that era had become increasingly difficult to pick or bypass through traditional mechanical manipulation. As safe technology advanced to become highly resistant to professional thieves, criminals shifted their tactics away from attacking the lock mechanism itself and toward coercing the individuals who held the means of access.1

To counter this rise in criminal coercion, James Sargent of Rochester, New York, developed a time lock in 1873. This device incorporated a clock mechanism that prevented the safe from being opened, even with the correct key or combination, until a pre-set time had elapsed.1