A.T. Robertson Commentary Mark 15:10

"For he perceived that for envy the chief priests had delivered him up." — Mark 15:10 (ASV)

He perceived (εγινωσκεν). Imperfect tense descriptive of Pilate's growing apprehension from their conduct which increased his intuitive impression at the start. It was gradually dawning on him. Both Mark and Matthew give "envy" (φθονον) as the primary motive of the Sanhedrin. Pilate probably had heard of the popularity of Jesus by reason of the triumphal entry and the temple teaching.

Had delivered (παραδεδωκεισαν). Past perfect indicative without augment where Mt 27:18 has the first aorist (kappa aorist) indicative παρεδωκαν, not preserving the distinction made by Mark. The aorist is never used "as" a past perfect.