Heb 2:3
So what makes us think we can escape if we ignore this great salvation that was first announced by the Lord Jesus himself and then delivered to us (hypo) those who heard him speak?
Here the author argues that his take on soteriology was passed to his contemporary Christians 'by' (hypó (a preposition) – properly, under, often meaning "under authority") those who heard (the Lord) speak. This may be simply rhetorical, saying the tradition had been passed to them from first generation of Christians. Clearly this is not Paul. He adamantly denied getting his take on Christianity from others but rather directly from Christ. It makes much more sense to identify the author with a later period.