Gregory the Great — as excerpted in the Catena Aurea on Matthew 10:16-18

“(Hom. in Ev. xxxv. 2.) Either that they had persecuted to the death, or that they had seen and were not changed. For the death of the saints is to the good an aid, to the bad a testimony; that thus the wicked may perish without excuse in that from which the elect take example and live.”