Earliest non biblical written source (which contains non written sources) attesting to the basic facts of Jesus’ life and death.
The Creed Paul recites in 1 Corinthians 15
“Christ died for our sins according to the scriptures, and that he was buried, and that he was raised on the third day according to the scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred of the brothers and sisters at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles.”
Significance of this short Creed:
1. Composed at the very latest 2 years after Jesus’ death and resurrection, most likely within several months of the events it recounts
2. Jesus is identified as the Messiah of Israel
3. Jesus died, which means a) he lived prior to dying b) therefore he existed
4. His death was an atoning sacrifice and understood as being prophesied about in the Tanakh
5. He was buried, because he died
6. And 3 days later he came back to life which is also understood as fully in accord with the prophecy in the Tanakh
7. Peter saw him alive again (2 non biblical sources)
8. The other 12 disciples also saw him alive again (13 non biblical sources)
9. Then more than 500 others saw Jesus alive again (513+ sources) and many are still alive so these facts can be verified
10. The brother of Jesus, James, also saw him alive again (514+ sources)
Jesus clearly existed. This is more than enough to establish that fact.