Acts 3:15

But the Prince of life ye killed

(τον δε αρχηγον της ζωης απεκτεινατε). "The magnificent antithesis" (Bengel) Peter here draws between their asking for a murderer and killing the Prince (or Author) of life. Peter pictures Jesus as the source of all life as is done in John 1:1-18; Colossians 1:14-20; Hebrews 1:2. Αρχηγος (αρχη, beginning, αγω, to lead) is an adjective "furnishing the first cause or occasion" in Euripides, Plato. Thence substantive, the originator, the leader, the pioneer as of Jesus both Beginner and Finisher (Hebrews 12:2). See also Hebrews 2:10; Acts 5:31 where it is applied to Jesus as "Prince and Saviour." But God raised him from the dead in contrast to what they had done.Whereof we are witnesses

(ου ημεις μαρτυρες εσμεν). Of which fact (the resurrection) or of whom as risen, ου having the same form in the genitive singular for masculine or neuter. Peter had boldly claimed that all the 120 have seen the Risen Christ. There is no denial of that claim.