Early in the 21st Century, THE TYRELL CORPORATION advanced Robot evolution into the NEXUS phase, a being virtually identical to a human known as a Replicant.
The NEXUS 6 Replicants were superior in strength and aglity, and at least equal in intelligeance, to the genetic engineers who created them. Special police squads – BLADE RUNNER UNITS – had orders to shoot to kill, upon detection, any trespassing Replicant.
This was not called execution. It was called retirement.