in 1994, Biden received a death threat in a letter postmarked from Worcester, Mass., that prompted an FBI investigation. "Dear Sen. Biden: You are a traitor …," the letter said, according to the FBI records. It was signed, "John F. Kennedy Jr." "The FBI dismissed it as a hoax," said Steven M. Gillon, professor of history at the University of Oklahoma and author of a recent biography about Kennedy, adding that the FBI chose not to pursue the letter "because they did not believe that John wrote it."
Gillon said he got access through a lawsuit to thousands of pages of documents related to Kennedy’s life and death, which he reviewed while writing his biography. The documents were mostly about Kennedy’s death, Gillon told us, but some were about threats against him.
"There is no mention, none at all, of a Biden attempt to kidnap JFK Jr.," Gillon said. "The statement (in the Facebook post) is false."
https://www.politifact.com/factchecks/2020/apr/27/facebook-posts/biden-plotted-kidnap-john-f-kennedy-jr-another-uns/