Witnessed (6)
'witnessed' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for seen that I've seen before include "Observed or percieved" , "Sighted" , "Met - understood" , "Perceived by sight" , "Distinguished" .)
(Other definitions for beheld that I've seen before include "Laid eyes on" , "watched" , "Seen" , "Saw or observed in olden times" .)