What is the evidence that Thomas Aquinas was assassinated? Reading the Wikipedia article on Thomas Aquinas, I stumbled on something rather peculiar.  Apparently he fell ill and died at the age of 49 on his way to the Second Council of Lyon, where he had been summoned by the pope to participate in an effort to reunite the Western and Eastern churches.

Maybe I'm a bit jaded, but it seemed fishy to me that a preeminent scholar "just so happened" to die on his way to such an important event.  I was thus pleased to note that the great Dante had similar misgivings: he wrote in the Divine Comedy that:


  Charles came to Italy, and for amends / A victim made of Conradin, and then
  / Thrust Thomas back to heaven, for amends. (Purgatorio, 20.67–69)


"Charles" here is apparently Charles I of Naples.  Wikipedia cites a historian who disputes Dante's speculations, but I'm not giving up so easily.  

What is the evidence, if any, that Aquinas was assassinated?
A recent biographer of St. Thomas, Jean-Pierre Torrell, says in Saint Thomas Aquinas. Volume I, The Person and His Work (Washington, D.C.: Catholic University of America Press, 2005), p. 294:


  The rumor must have circulated rather widely; the chronicler Giovanni Villani and Dante Alighieri himself echo it. It seems that all the historians are in agreement today in discarding this rumor as without serious foundation.