From Vince Bugliosi's RECLAIMING HISTORY: (Footnotes on CD)

A former Chicago Secret Service agent, Abraham Bolden, told HSCA staff
investigators that shortly before November 2, the FBI sent a Teletype message to
the Chicago Secret Service office stating that there would be an attempt on
Kennedy’s life in Chicago on November 2 by a four-man hit team using highpowered
rifles (HSCA Record 180-10070-10273, January 19, 1978, pp.2–6). The
HSCA said it “was unable to document the existence of the alleged assassination
team. Specifically, no agent who had been assigned to Chicago confirmed any aspect
of Bolden’s version.” The HSCA said that “one agent did state there had been a
threat in Chicago during that period [not uncommon, of course], but he was unable
to recall details.” The HSCA concluded that Bolden’s story was of “questionable
authenticity.” In 1964, Bolden was prosecuted and convicted of conspiring to sell
official information in a counterfeiting case and was sentenced to six years in prison.
(HSCA Report, pp.231–232; Waldron with Hartmann, Ultimate Sacrifice, pp.
258–259, 649–650; New York Times, December 6, 1967, p.26; HSCA Record 180-
10070-10273, January 19, 1978, p.2)