First, Jesus' execution is reported in a number of ancient sources: Christian and non-Christian. In addition to the four Gospels and a number of letters contained in the New Testament, all of which were written in the first century, Jesus' execution is even reported by a number of ancient non-Christian sources. Josephus (late first century), Tacitus (early second century), Lucian (early to mid second century), and Mara bar Serapion (second to third centuries) all report the event. The fact that these non-Christians mentioned Jesus in their writings shows that Jesus' death was known outside of Christian circles and was not something the Christians invented.Regarding the non-Christian sources, Licona is plainly mistaken. The fact that the story of Jesus' crucifixion became known outside Christian circles sixty years later does not in any way show that Christians didn't invent it.
Regarding the Christian sources, I am struck by a comment Licona made about Matthew 28:16 in The Resurrection of Jesus: A New Historiographical Approach. In that passage, the disciples go to Galilee to meet the resurrected Jesus and "When they saw him, they worshiped him; but some doubted." Licona suggests that one possibility is that it was not any of the disciples who doubted, but outsiders who just happened to be present:
In the back of the crowd one man says to another, "What is all the excitement about? We have heard Jesus before. What is so special this time?" The other answers, "Didn't you hear? Jesus was crucified last Friday in Jerusalem and he has risen from the dead!" The first is skeptical of the report and says, "Someone got things wrong. The Romans must have crucified someone else."This strikes me as an eminently sensible analysis. The very fact that Jesus is walking around and talking is an excellent reason for doubting that he had been crucified. I can easily imagine that same skeptical fellow asking "Did any of you see Jesus being crucified?" The disciples might have honestly replied "No. After Jesus was arrested, we went into hiding," after which, the skeptical fellow would have been fully justified in remaining skeptical.