Surely "you have his blood on your hand" is also correct? The given answer (hands plural) presumably is figurative.
But the Czech sentences also uses the plural (well, technically dual but let's not get into that :D)!
Why wasn't hand in the locative case?
It is. You need the peculiar dual endings for body parts here. Check the tips and notes.
Is the Czech sentence literal or figurative?
Could be either in either language.