Here is the case of Michael Musbach, who hired a hitman over the internet on a murder-for-hire website, paying him $20,000 to kill his target. When he was asked to make additional payments, he sought to cancel the contract and get a refund, at which point the "hitman" revealed the whole site was a scam and sent his information to the authorities. Even though Musbach never actually hired a real hitman, and sought to cancel the hit before any damage was done, he was found guilty of "knowingly and intentionally using... a facility of interstate and foreign commerce with the intent that a murder be committed."
The use of the internet made this an interstate federal crime, but Musbach's actions based on the mere intent to arrange a murder was sufficient convict him, regardless of whether he was successful or later thought better of it. Other statutes may apply when hiring a local hitman.