—Pharisees and “experts in the law” did because he threatened the religious establishment and its control over the masses.—
This is where things get really fishy for me. If you read the Synoptic Gospels, you notice that the Romans come off in a very good light: several positive examples: even Pilate (who other accounts describe as a vicious tyrant) wishes to be merciful, but is to some degree powerless. This in itself is suspicious, especially if Mark was indeed written very soon after the Romans crushed the rebellion and destroyed the temple (probably the most horrific thing they could have done).
It becomes even more fishy considering what we know about the Pharisees outside of the Gospels: namely that their philosophy was much much closer to that which Jesus seems to hold than almost any other group (sometimes with Jesus leveling criticisms at Pharisees that are exactly what Pharisees criticized others for): certainly the Sadducees, who were… the Roman toady faction.
Certainly, there’s not enough here to draw conclusions, but consider this scenario…
Jesus, the real Jesus was actually on the side of the Pharisees, making their sorts of social and theological criticisms of the Jewish leadership, which was dominated by the anti-rebellion Sadducees. He was essentially condemned for rebelling against Rome, and the Romans and Jewish Roman sympathizers had him put to death like most such rebel Messiahs.
His leftover followers, expanding his myth in the wake his death, invert his original purpose: taking the only interperative route they can think of to continue to venerate him: making his death actually the intended victory instead of an unexpected defeat. In the meantime, this causes a split with the Pharisees, who still want a successful rebellion, but whom the Jesus people start to reject as holding the old view of the messiah that is threatening to Jesus’ new meaning.
So when the Pharisees eventually wind up leading Judea into a failed rebellion that ends up getting the Temple, one of the most important icons in that day, destroyed, they fall out of favor in a BIG way: which leads to even more rationale for blaming the Pharisees even as far back to Jesus’ day. In the new Roman dominated Judea, Jesus’s Pharisee alignment is by this time all but washed away (being a Pharisee at this point would be the most unPC position imaginable, as well as pissing off the Romans): instead the story is that the Pharisees were the real problem. In the new Roman dominated culture, the Romans of course have to come off well if the story has any chance of being tolerated is going to tolerate the story, and by proxy, the more pro-Roman Sadducees have to come off moderately well too. The Pharisees have now become the stalwart villians of the story: laughable buffoons that turn violent in the end. This explains why their Gospel portrayal is inconsistent with what we know about their actual positions, and why the stupid views they hold are far closer to what they objected to coming from the Sadducees.
Paul then becomes an interesting case, for there was always something fishy about his claim to have been a Pharisee: his writings show little evidence of such a litterary training.
Instead, the story seems to be that, to impress the Jewish father of his paramour, he had to undertake Pharisee training, but flunked out, and in hatred he turned on them. Instead of being a Pharisee, he was working for Rome against BOTH the Pharisees AND early Christians (which is, as far as we can tell, what was actually going on with the guy he claimed to be working for). This also explains why Paul, who wrote far earlier than the Gospels, is so ignorant of Jesus’ life story: it hadn’t been reformulated yet. All that was present was the split between the Pharisees and the early Christians: which also goes alot to help explain his own major discontent with other early Christians, who were far closer to the old Pharisee view than Pauls’ new anti-Jewish tradition split.
All speculative, of course, but certainly interesting to think about.