Commentary for Makkot 4:5

And just as a (false witnesses) who (causes someone) to be stoned (note: past tense), do not themselves get stoned - Witnesses who are not found to be false prior the accused being killed, and after (the death of the falsely accused) are found to be false, are not killed, as we state later in this chapter (Daf 5b), If they kill they ae not killed, as it is written in Scriptures 'as they intended' (from which is derived) and not as they have done:

One who comes to stone and does not stone - That he is found to be false prior to the accused being killed:

He that did an act intentionally does not go into exile - A killer that did a deed, if he acted with intent, he does not go into exile, and even in a situation (lit. a time) that he is not killed, for example it was premeditated, (but) without (appropriate) warning (by witnesses):

They (the false witnesses) that did not do a deed - Rather (their action) was only verbal, and (although) their testimony was premeditated, is it not logical they should not go into exile for their premeditated intention: