[AmusedBystander]

The Templars knew too much of the sacred mysteries of alchemy and knowledge of the the lost Teachings of Jesus, which knowledge could empower men to defeat their overlords

I guess that knowledge wasn't too powerful. It couldn't overcome a medieval king of France.

[bert]

It couldn't overcome a medieval king of France....

The specific King in question committed the murders on contract to the Pope, the head man of the Roman Catholic Church. The RCC has the blood stained hands for the Templar murders.

[Rennes Templar]

The knowledge was powerful. They never thought they would have to use it against those they had served, ie the church. They could not conceive that the church would be an enemy, ie be infiltrated by overlords (fallen angels) of the same variety that hey were fighting on other fronts. Thus many didn't fight back, either out of total dismay, or due to the goodness within them.