The Pendle witches weren't just accused of witchcraft as at Salem. They practiced it.
They boasted of their power to kill and sterilize people with magic - and they gave themselves occult names to deliberately inspire fear in others.
They went on trial when one group of witches denounced another to the authorities hoping to eliminate the competition for lucrative crop and fertility spells.
It backfired, and the authorities tried both sides.
When multiple witnesses have heard you brag that you are responsible for a sudden, explained death or two, you can find yourself in trouble.
It is not the law's job to scientifically prove that you could not have deliberately caused a death that you yourself have publicly boasted of causing.
http://en.wikipedia.org/wiki/Chronological_snobbery
These days we have a much higher tone of misconceptions and prejudices.