Board Thread:Legitimate Canon Questions/@comment-25178327-20140205162328/@comment-4091815-20140205171957

They were all standing around together and saw Peter and Derek go in for the kill on Jackson together.

They were then all present when Jackson died and came back so barring some major distraction on their part - they saw him alive.

You are correct in that it hasn't been directly addressed on the show - we've seen Melissa and Scott surprise face at seeing him but that's it.