The strain of His death overwhelmed them. That's right, over 500 victims of mass hysteria and hallucinations, along with Roman officials, military officers, temple guard, Jewish leaders and the like. Educated, enlightened people have to stretch to expect reasonable people to accept this theory. Perhaps some question the validity of the resurrection of Christ, along with other miracles and divine acts, because the presented evidence is contained in the same book where the event is first noted. In other words, an alleged event, such as the resurrection of Christ, should be supported by other sources.
Many people assume the Bible is just one source.
This is a legitimate concern. The Bible is just one volume today. It was written by at least eight authors and an unknown number of contributors. It was hundreds of years before these separate and independent accounts were consolidated into one easy to use volume. This was done for convenience of study and because of common inspiration.