This is the passage from the "Gospel of Thomas", edited by Benton Layton
http://www.earlychristianwritings.com/thomas/gospelthomas65.html
http://gnosis.org/naghamm/thomas_poxy.htm
LAYTON
(65) He said, "A kind man owned a vineyard, and put it in the hands of cultivators for them to cultivate, so that he might get its produce from them. He sent his slave so the cultivators might give the produce of the vineyard to the slave. They seized, beat, and all but killed his slave, and the slave went and spoke to its owner. Its owner said, 'Perhaps they did not recognize it (the slave),' and he sent another slave. The cultivators beat the other slave. Next the owner sent his son and said, 'Perhaps they will show respect for my son.' Those cultivators, since they recognized that it was he who was heir to the vineyard, seized him and killed him. Whoever has ears should listen!"
However the "killing of the Son" is included also in this version. Therefore supposedly the story or parable has a very early origin. The other gospel writers put the parable in a scene - the dispute with the pharaseans and highpriest - and write that they understood that they were meant as evil tenants, what in the Gospel of Thomas is not the case though.
However the "The killing of the son" part of the story may have been part of the original saying of the 1st century church reflecting and giving sense to Jesus death. But in the interpreation of the parable the death of Jesus is not the main aspect at all.
Most commentaries write that it turns about a lession of the kingdom of God, namely that God awaits his people to bear fruits in the vineyard and living in the kingdom means living as we had only the last chance too to show respect for what he gifted us as our portion of his vineyard.
Examplary comment:
God is in the parable also pictured as "winegrower" who knows of the fail of the vineyard Israel (Isa 5) Once more God lets decide the people if they want to shape their lifes in accordance with God.But as in the parable of Adam and Eve who secretly ate what was not entitled to them, here men publicly and forced want to take life and its fruits in their hands. Both times the human wish to be "heirs of God" ends in death and expulsion, there from the paradise, here from the vineyard. Although this time even the "Son" was sent they forgot that without God they would have harvested nothing.
The parable is a story about a often newly granted chance.