There are many Jews today that believe that Jesus is the Christ and their promised deliverer. In fact, Jesus had multitudes of Jewish followers and the entire Bible is written by Jews. It is written in the Holy Scriptures that Salvation comes through the Jews. Jesus Christ is a Jew. In fact, it was the leadership of Israel in Jesus' day when He walked on earth that did not accept Him,(the Pharisees and Sadducees because they did not want to give up their power to Him), BUT WITHOUT A DOUBT, THEY KNEW WHO HE WAS!!
In the Gospel of Matthew, Jesus said unto them:
"But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, 'O generation of vipers, who hath warned you to flee from the wrath to
come?"
"the entire Bible is written by Jews."
Except for Luke-Acts, you are correct.
And your source for this is, what exactly? The gospels and epistles of the Christian scriptures? I expect you'll disagree, but I don't think we can count on them to give a fair and accurate depiction of Judaism and Jewish reaction to the early Christian movement. These are polemical works, advancing their own particular viewpoints. They are not objective histories.
They knew the individual. They certainly did not "know" him as the "Son of God" (utter blasphemy) but as a one of many messianic claimants.