This is a point worth reiterating over and over again. People those days remained unconvinced that Jesus was the Messiah. If they were, then a lot of the Jews should have became Christians immediately when evidence suggesting so were all 'fresh'. Instead, it took 70 years, that is roughly two lifetimes for most people then, for the early Saul/Paul to promote Jesus as the Messiah prophesied by the Old Testament. This is way too long for any sort of reliable evidence to be gathered about the life of this person named Jesus.
Do you have a different answer that might help the questioner? How would you answer this question?