If you read How Is The Date Of Easter Calculated? The Science Answer you learned about astronomy and why Christians established the paschal full moon after the vernal equinox as Easter - Christ was resurrected on a Sunday and died on a Friday, the paschal full moon was the date of Passover in the Jewish calendar, and the Last Supper (what Christians call Holy Thursday) occurred on the Passover. 

Prof. Colin Humphreys of Cambridge University says that isn't so and discrepancies among the Gospels happened because they used an older calendar than the official Jewish one.   His claim: the date was instead April 1st, 33 A.D.

The Gospels of Matthew, Mark and Luke say the Last Supper coincided with Passover, but John claims it took place before Passover.  Humphreys says an arrest, interrogation and separate trials jammed into one evening and morning were difficult to accept but if Matthew, Mark and Luke used the older Jewish calendar adapted from Egyptian usage at the time of Moses rather than the official lunar calendar John might have used, "the four gospels agree perfectly." 

If the the date was April 1, 33, according to the standard Julian calendar, Humphreys says the case can be made for giving Easter a permanent date as the first Sunday in April.