Because they knew him not (touton agnoēsantes). First aorist active participle (causal) of agnoeō, old verb, not to know. Peter gives “ignorance” (agnoia) as the excuse of the Jews in the death of Christ (Act 3:17) and Paul does the same about his conduct before his conversion (1Ti 1:13). This ignorance mitigated the degree of their guilt, but it did not remove it, for it was willing ignorance and prejudice.
The voices of the prophets which are read (tas phōnas tōn prophētōn tas anaginōskomenas). Object also of agnoēsantes, though it could be the object of eplērōsan (fulfilled) if kai is taken as “also”. The “voices” were heard as they were read aloud each Sabbath in the synagogue. In their ignorant condemnation they fulfilled the prophecies about the suffering Messiah.