GREENVILLE, N.C. — Some parts of Abraham Lincoln's life remains a mystery, including an assassination attempt he may have plotted.

Lincoln historian and East Carolina professor David Long believes Jefferson Davis made very clear that the South would never surrender short of independence. Long also believes Lincoln was determined to prevail.

Long believes Lincoln authorized a group headed by Col. Ulrich Dahlgren to kill Davis. However, that attempt failed and Confederate soldiers found documents on Dahlgren's body detailing the alleged plot.

"The Confederates now believe, 'That's what they're doing. We'll do the same thing,'" Long said.

Enter John Wilkes Booth.

"He's an actor. He's going to make his grand moment on stage -- the assassination of the president of the United States," Long said.

Long said Lincoln's alleged plot is more than just a theory, but fact.

"It does not change my attitude of him. If anything, it expands Lincoln," he said.

Long's book about the raid and the Lincoln/Jefferson Davis assassination theory is due out this summer.