Italy must be where all criminals go to hide. John Surratt, Confederate Soldier, was was a fugitive, wanted for his connection to the Lincoln Assassination fled to Italy, and got a position as a Swiss Guard at the Vatican. In the meantime, his mother was hanged for her part.
Having been an associate of Booth's in the earlier kidnapping plan, however, Surratt could reasonably have expected to hang along with everyone else. He left the country. He did enlist in the Swiss Guards, though he did so under a false name, and I am not aware that the papal authorities had any idea who he was.
As it turned out, the investigations and trials following Lincoln's assassination were a model of restraint. Most governments throughout history would have conducted a broad sweep followed by drumhead trials and wholesale executions. In this case, however, the authorities were remarkably precise and highly disciplined. The assassinators were hung. A small group of Booth collaborators not directly linked to the assassination (e.g. kidnapping plot participants who took no part in the assassination) were convicted and sent to prison for varying terms; this is how Dr. Mudd got his all-expenses-paid visit to the Florida Keys, where he distinguished himself in a yellow fever epidemic and won a commutation. Nothing at all was done to a larger number of Booth collaborators who had been members of the confederate underground during the war but who had no involvement in the two plots against Lincoln.