CIA Deputy Director Richard Helms signed an affidavit that the covert photo of "Saul" were taken Oct. 4, 1963 outside of the Russian Embassy. The photo was intro'd in the Warren Commission as Exhibit #237. It was relevant to the Commission because, per McDonald:
"On the morning of November 22, 1963, before the assassination, a copy of that picture was received by the FBI in Dallas, Texas. The picture was identified as possibly being Lee Harvey Oswald. The FBI agents in Dallas knew Lee Harvey Oswald and they knew that the photograph forwarded them was not a picture of Oswald. At the time this error in identity did not seem important. However, things changed radically after the killing of President Kennedy and the apprehension of Oswald for that crime." (McDonald, as told to Geoffrey Bocca, Appointment in Dallas: The Final Solution to the Assassination of JFK, 1975, p. 54)
The book references "secret FBI reports" where it appeared that three pictures of this "mystery man were shown to a Mexican national, Mr. Pedro Gutierrez Valencia. They were shown to him hoping that he could identify the man in the picture. He could not...The unidentified man in the photograph became important as a possible co-conspirator of Oswald..." (p. 56)
The book publishes the cropped pictures of "Saul" (pp. 53, 55, 57).
See: "Saul" (Warning: This also includes graphic autopsy photos of President Kennedy)
Two FBI photos are here: "Saul" in Mexico City
The facial features are similar to the "Identi-Kit" Model II composite of "Saul" compiled by Hugh McDonald based upon his memory of the 1972 meeting with him as the Westbury Hotel in London. (p. 59 of the book)
McDonald claimed that this 1972 "contact" told him Oswald fired 3 shots; himself, 2. And that he was in a position to see Oswald at his position...and was ready for some law enforcement agent to return fire toward Oswald, at which point he was prepared to take out Oswald himself.
From the details, McDonald claims the other assassin fired from a second floor window of the County Records Building. [The link above pinpoints it as a corner room]
I've heard other plausible accounts of an additional shooter from the picket fence behind the grassy knoll...and even one account of a shooter being in a ground-level/below ground-level storm drain.
(It wouldn't surprise me, either, if one hired assassin wasn't told about another on the scene)
If he was told this, why didn't he arrest him on the spot?
For the record, one of those “autopsy” photos, Jfk on the gurney, is from the movie JFK. The one right above the caption “Autopsy photos of President John Fitzgerald Kennedy” on that webpage: http://www.geocities.ws/jfktruth/