Here is what Paul L. Williams wrote about Siri in his book "The Vatican Exposed"
The sources for the declassified State department files are sourced at the end.
Is this guy making it up? Can't anybody who wants access these files?
In 1954 Count Della Torre, editor of the Vatican newspaper L'Osservatore Romano, warned [Pope] Pius XII of [Cardinal Angelo] Roncalli's Communist sympathies. Other members of the "Black Nobility" expressed similar concerns.[5]
Nor did Roncalli [later known as "Pope John XXIII"] escape the attention of the FBI and CIA. The agencies began to accuмulate thick files on him and the questionable activities of other "progressives" within the Vatican, including Monsignor Giovanni Battista Montini (the future Paul VI).
[...]
Pius XII had appointed Cardinal Giuseppe Siri as his desired successor.[7] Siri was rabidly anti-Communist, an intransigent traditionalist in matters of church doctrine, and a skilled bureaucrat. . . .
In 1958 [on October 26], when the cardinals were locked away in the Sistine Chapel to elect a new pope, mysterious events began to unfold. On the third ballot, Siri, according to FBI sources, obtained the necessary votes and was elected as Pope Gregory XVII.[8] White smoke poured from the chimney of the chapel to inform the faithful that a new pope had been chosen. The news was announced with joy at 6 P.M. on Vatican radio. The announcer said, "The smoke is white. . . . There is absolutely no doubt. A pope has been elected."[9] . . .
But the new pope failed to appear. Question began to arise whether the smoke was white or gray. To quell such doubts, Monsignor Santaro, secretary of the Conclave of Cardinals, informed the press that the smoke, indeed, had been white and that a new pope had been elected. The waiting continued. By evening Vatican radio announced that the results remained uncertain. On October 27, 1958, the Houston Post headlined: "Cardinals Fail to elect pope in 4 Ballots: Mix-Up in Smoke Signals Cause False Reports."[10]
But the reports had been valid. On the fourth ballot, according to FBI sources, Siri again obtained the necessary votes and was elected supreme pontiff. But the French cardinals annulled the results, claiming that the election would cause widespread riots and the assassination of several prominent bishops behind the Iron Curtain.[11]
The cardinals opted to elect Cardinal Frederico Tedischini as a "transitional pope," but Tedischini was too ill to accept the position.
Finally, on the third day of balloting, Roncalli received the necessary support to become Pope John XXIII. . . .
--Paul L. Williams, The Vatican Exposed (Amherst, NY: Prometheus Books, 2003), pp. 90-92
The footnote numbers included in Williams' text point to the following references (adapted from p. 243):
• [5] Department of State confidential biography, "John XXIII," issue date: no date, declassified: February 15, 1974; see also Avro Manhattan, Murder in the Vatican, p. 31.
• [7] John Cooney, The American Pope, p. 259.
• [8] Department of State secret dispatch, "John XXIII," issue date: November 20, 1958, declassified: November 11, 1974.
• [9] The announcer's words appeared in the London Tablet, November 1, 1958, p. 387.
[11] Department of State Secret File, “Cardinal Siri,” issue date April 10, 1961, declassified: February 28, 1994]