During Jesus's time, the Temple in Jerusalem was under the control of a group of priests who were Pharasees.  The Pharasees were a minority sect of Judaism heavily influenced by ideas from Persia ("Pharasee" = "Persian&quot and they weren't at all in the mainstream of most Jews at the time. 

But the Pharasees did control the temple, and they had made up a bunch of rules that basically forced people to pay a lot of money for absolution.  You had to buy all kinds of different animals for sacrifice and pay fees to have them purified and all that, so they had a stranglehold and a monopoly on the business of forgiving sins.  Ever wonder why there were money-changers in the temple yard?  They were providing financial services for pilgrims who had come to buy absolution for sins.

When he came and basically said "you don't need to sacrifice animals for absolution anymore," Jesus threatened the livelihood of the Pharasee priesthood.  So they had the Romans kill him.  So it was a sectarian killing.

We don't have information for sure about what kind of Jew Jesus was (assuming that he was a real person).  But many details in the gospels, like the fact that he was a "carpenter" (actually a migrant generic laborer) and the whole baptism thing suggest that he might have belonged to one of the progressive, apocalyptic sects like the Essenes.  These guys believed that the end of the world was immanent, and that baptism--rather than animal sacrifice--was the path to absolution.

Paul of Tarsus, incidentally, was also a Pharasee before his big conversion experience.  It accounts for his obsession with sin and absolution, which were really mostly Persian ideas. 

I thought that according to the Bible myth that Jesus was sent by his father to Earth so that he would be be killed and die for man's sins. If this was god's plan then isnt he responsible?

As Robert Ingersoll pointed out, God told the Jews to execute anyone who tried to change the OT laws, and Jesus came down to change them - so they were only doing what he said. God/Jesus only reaped what he sowed.

Why thank you, Christos (and Wavefreak).

It was always a big issue for me growing up and reading the Gospels and trying to make sense out of what was going on.  Read, as I was taught, that they're the story of Jesus coming to establish a new covenant with gentiles, the canonical Gospels make no sense at all (except maybe some parts of John).  Read as the story of Jesus, the radical Jewish reformer trying to fix the problems with his own religion, it all falls into place.