Evil idea :D
They say that the matter brought back from the future disappears when the future version enters our dimension. Instead of chasing people whom they know, they could extract e.g. the brain or the heart from the evil guys bodies and bring them back to the past :D Imagine evil guy doing something, and then - bang - he's got no legs and arms :D They don't have to be full limbs, just cut out thin slices and watch the evil guys fall apart ]:D