The Rambam discusses cases which I believe are what you call conspiracy (MT Rotzeach uShmirat Nefesh 2:2)
But a person who hires a murderer to kill a colleague, one who sends
his servants and they kill him, one who binds a colleague and leaves
him before a lion or the like and the beast kills him, and a person
who commits suicide are all considered to be shedders of blood; the
sin of bloodshed is upon their hands, and they are liable for death at
the hands of God. They are not, however, liable for execution by the
Then in 2:4
When a Jewish king desires to slay any of these murderers and the like
- who are not liable for execution by the court - by virtue of his regal authority, in order to perfect society, he has the license.
Similarly, if the court desires to execute them as a result of a
immediate fiat, because this was required at the time, they have the
license to do as they see fit.
If the king did not execute them, nor did the court deem the time as
such to require strengthening the strictures against murder, it should
nevertheless have the murderer beaten with severe blows - so that he
is on the verge of death - and imprisoned, deprived and afflicted with
all types of discomfort in order to strike fear and awe into the
hearts of other wicked men, so that this death should not be a
stumbling block and a snag for them, causing them to say: "Let me
arrange to have my enemies killed the way so-and-so did, and I will
not suffer the consequences."