He could calculate the amount of blood lost by a man who was dead, or by one who was only wounded.

That night three men had fallen, either dead or wounded.

What were the probabilities?
The two stains in the choir to the right and left of the pedestal were probably the blood of Sir John's two antagonists.

That on the pedestal was probably his own.

Attacked on both sides, right and left, he had fired with both hands, killing or wounding a man with each shot.