He looked (emblepsas). First aorist active participle of emblepō, antecedent action before legei (says).
As he walked (peripatounti). Present active participle in dative case after emblepsas and like erchomenon in Joh 1:29 vividly pictures the rapture of John in this vision of Jesus, so far as we know the third and last glimpse of Jesus by John (the baptism, Joh 1:29, and here).
Saith (legei). Historical present, change from histēkei before. He repeats part of the tribute in Joh 1:29.