the Jesuits did it

 Yes. I am being sarcastic.

At a time when the JFK files are inflaming every nutcase conspiracy theory, maybe looking into older conspiracy theories should be seen and put into contrast to today's news.

First, the background of the assasination is discussed here:

...

So where do the Jesuits come into the plot with an infamous conspiracy theory?

 it starts with the dirty little secret that Catholics are disliked and outsiders in the USA back then, and immigrants (many of whom were Irish Catholics) were greatly disliked. 

This should give one pause, since there are parallels in today's world, where immigrants and Muslims are outsiders and greatly disliked.

 and then there is this: John Wilkes Booth was a Catholic convert, many of those involved had Catholic links, and Mary Suratt's son escaped with the help of Canadian Catholics.

more from NatCathRegister:

all the conspirators met at the boarding house owned by Mary Surratt. Mary Jenkins Surratt was a Catholic, having converted before her marriage to John Surratt in 1840. Everyone who had rooms in her house was a Catholic. Her son John, Jr.—who escaped capture and trial for a time by seeking sanctuary in a Montreal church rectory and then as a Papal Zouave—was a Catholic...  Another accomplice, David Herold, had studied at Catholic colleges including Georgetown. Dr. Samuel Mudd, who set Booth’s broken leg, was a Catholic.  

So far we only have a bunch of confederate sympathizers who happen to be Catholic. 

 so where do the Jesuits come into this?

fast forward to Charles Chiniquy's theory of Lincoln's Assassination. Why would the Jesuits do such a thing? Because Lincoln had once been hired by him as a lawyer to defend him against libel charges.

duh. 

Does one sort of wonder at the grandiosity of a person making such a claim? Why would Jesuits do this to revenge a guy who was in trouble not just with the law but with his bishop, and who later made a living writing Anti Catholic propaganda?

Nope that doesn't make sense... But hey conspiracy theorists don't have to make sense: they just cherry pick some details and weave the story from one sided minor details to confirm their prejudices.

And back then, lot of folks back then automatically believed Catholics were bad in the same way that there are lots of people out there who hate Muslims or immigrants with brown skin, not for their deeds but because a small minority of them commit crimes.

But like in today's world, conspiracy theory theorists can get rich off by pushing their ideas.

Indeed, Chiniquy made a good living being a professional anti Catholic at a time when anti (Irish Catholic) immigration feelings were high, and his paranoid fantasies continue to be recycled by professional Anti Catholic Jack Chick.

Irish Central has an article about the anti Irish/anti Catholic hysteria at that time helped the public assume Mary Surrat was guilty:

backstory: Her silence enabled her son, who was involved in earlier plots but not in this one, escape.

so a Catholic conspiracy, or just a loving mother willing to do so that her son escape a lynch mob mentality of the courts?

 Robert Redford has a movie about it: