Was there an assassin on Grant's train?

[RJNorton]

(05-21-2015 12:11 PM)Wild Bill Wrote:  Richmond sent powderman Thomas Harney to blow up the White house. But Harney was captured just outside Washington. He was to be led into the Whitehouse basement by Booth and his compatriots. Now Booth wondered where Harney was, found him in the Old Capitol Prison though informants, and decided to do Harney’s job for him. Explosives were beyond the ken of Booth and his men so they reverted to normal weapons—revolvers, knives. The targets were Lincoln (Booth), Johnson (Atzerodt), Seward (Powell), Stanton (Olaughlen), and Grant (Surratt). So Booth and his cohorts carried out a MILITARY OPERATION to nullify the C3I of the Union Forces in the field. At the time only Lee’s army had surrendered, and his was the smallest force in the field for the Confederacy.

I found what Bill said about John Surratt most interesting as we have debated John Surratt's whereabouts on the 14th in other threads. We have also debated whether or not Grant was targeted for assassination. If Bill is right then John Surratt was in Washington (not Elmira), found out from Booth that Grant had changed plans (about the theater invitation), and then boarded the Grants' train with the intent of assassination (but did not succeed).

(For years I have gone back and forth regarding Surratt's whereabouts on the 14th)

In Beware the People Weeping Thomas Turner writes that Grant's son, Jesse, said that "his mother received a letter from someone claiming he was supposed to assassinate Grant, but had failed and been glad of it ever since. The general himself referred to a similar letter he received after the assassination, but he could not determine if it was genuine or not."

In her memoirs Julia Grant included the text of the anonymous letter her husband received shortly after the Lincoln assassination:

'General Grant, thank God, as I do, that you still live. It was your life that fell to my lot, and I followed you on the [railroad] cars. Your car door was locked, and thus you escaped me, thank God.'

Could John Surratt have sent these letters? If Surratt were in Elmira, who would Booth have assigned to kill Grant on the train? O'Laughlen?

Was there an assassin on Grant's train with the assignment to kill him?