Why did king Manasseh have Prophet Isaiah killed?

There are two rabinnic traditions, both of which describe how he was killed; in both cases he was ordered sawn in two by King (of Judah) Manesseh while in a cedar tree. This act is also indirectly referenced in the New Testament in Hebrews 11:27. But the bigger question, "Why?" requires a study from the Chronicles and from Isaiah's writings. Chronicles records that Manesseh tried to appease and worship the God of Israel, as well as the Canannite gods. He attended all of the Jewish sacrifices and worship, but also allowed some of his infant sons to be sacriced to the Cananite god Molech. Manesseh was a consumate politician, who led the small nation of Judah and walked a political tightrope between Assyria, Syria and Babylon for 55 years. Manesseh's actions were repeatedly condemned by God through the prophet Isaiah. Isaiah's writings are filled with strong Words against Manesseh, the ruling classes and even the priesthood. Manesseh most likely ordered a public execution of Isaiah in order to silence him.