The governor was going to release one prisoner (Mt 27:15-27:15)

“Now at the festival time,

The governor

Was accustomed

To release

A prisoner

To the crowd,

Anyone whom they wanted.”

 

Κατὰ δὲ ἑορτὴν εἰώθει ὁ ἡγεμὼν ἀπολύειν ἕνα τῷ ὄχλῳ δέσμιον ὃν ἤθελον

 

This is almost word for word in Mark, chapter 15:6.  In John, chapter 18:39, there is something similar about the custom of releasing prisoners, but there is nothing in Luke about this custom.  Matthew and Mark said that at the festival time, the Roman governor had the custom (Κατὰ δὲ ἑορτὴν εἰώθει ὁ ἡγεμὼν) to release one of the many prisoners to the crowd (ἀπολύειν ἕνα τῷ ὄχλῳ δέσμιον), usually it was not a criminal facing the death penalty.  This crowd could pick anyone that they wanted (ὃν ἤθελον), so that this kept the local folks happy.