Manny Pena served in the Pacific during the Second World War. He later worked as a counter-intelligence officer in Latin America and France before joining the Los Angeles Police Department (LAPD) in 1947.

Pena developed the reputation for being an aggressive police officer and is said to have killed eleven suspects "in the line of duty". According to his commanding officer, Pena was a "stocky, intense, proud man of Mexican-American descent."

In November 1967 Pena resigned from the LAPD to work for the Agency for International Development (AID). According to the San Fernando Valley Times: "As a public safety advisor, he will train and advise foreign police forces in investigative and administrative matters. Over the next year he worked with Daniel Mitrione in Latin and South America.

Charles A. O'Brien, California's Chief Deputy Attorney General, told William Turner that AID was being used as an "ultra-secret CIA unit" that was known to insiders as the "Department of Dirty Tricks" and that it was involved in teaching foreign intelligence agents the techniques of assassination.

FBI agent Roger LaJeunesse claimed that Pena had been carrying out CIA special assignments for at least ten years. This was confirmed by Pena's brother, a high school teacher, who told television journalist, Stan Bohrman, a similar story about his CIA activities. In April 1968 Pena surprisingly resigned from AID and returned to the LAPD.

On 6th June, 1968, Robert Kennedy won the Democratic Party primary in California obtaining 46.3% (Eugene McCarthy received 41.8%). On hearing the result Kennedy went down to the ballroom of the Ambassador Hotel to speak to his supporters. He commented on “the divisions, the violence, the disenchantment with our society; the divisions, whether it’s between blacks and whites, between the poor and the more affluent, or between age groups or on the war in Vietnam”. Kennedy claimed that the United States was “a great country, an unselfish country and a compassionate country” and that he had the ability to get people to work together to create a better society.

Robert Kennedy now began his journey to the Colonial Room where he was to hold a press conference. Someone suggested that Kennedy should take a short cut through the kitchen. Security guard Thane Eugene Cesar took hold of Kennedy’s right elbow to escort him through the room when Sirhan Sirhan opened fire. According to Los Angeles County coroner Thomas Noguchi, who performed the autopsy, all three bullets striking Kennedy entered from the rear, in a flight path from down to up, right to left. “Moreover, powder burns around the entry wound indicated that the fatal bullet was fired at less than one inch from the head and no more than two or three inches behind the right ear.”

Chief of Detectives Robert Houghton asked Chief of Homicide Detectives Hugh Brown to take charge of the investigation into the death of Robert Kennedy. Code-named Special Unit Senator (SUS). Houghton told Brown to investigate the possibility that there was a link between this death and those of John F. Kennedy and Martin Luther King.

As William Turner has pointed out in The Assassination of Robert F. Kennedy: "Houghton assertedly gave Brown free reign in electing the personnel for SUS - with one exception. He specifically designated Manny Pena, who was put in a position to control the daily flow and direction of the investigation. And his decision on all matters was final."

According to Dan E. Moldea (The Killing of Robert F. Kennedy), Houghton told the SUS team working on the case: "We're not going to have another Dallas here. I want you to act as if there was a conspiracy until we can prove that there wasn't one."

An eyewitness, Donald Schulman, went on CBS News to say that Sirhan “stepped out and fired three times; the security guard hit Kennedy three times.” As Dan E. Moldea pointed out: “The autopsy showed that three bullets had struck Kennedy from the right rear side, traveling at upward angles – shots that Shiran was never in a position to fire.”

Robert Kennedy had been shot at point-blank range from behind. Two shots entered his back and a third shot entered directly behind RFK’s right ear. None of the eyewitness claim that Sirhan Sirhan was able to fire his gun from close-range. One witness, Karl Uecker, who struggled with Shiran when he was firing his gun, provided a written statement in 1975 about what he saw: “There was a distance of at least one and one-half feet between the muzzle of Shiran’s gun and Senator Kennedy’s head. The revolver was directly in front of my nose. After Shiran’s second shot, I pushed the hand that held the revolver down, and pushed him onto the steam table. There is no way that the shots described in the autopsy could have come from Shiran’s gun. When I told this to the authorities, they told me that I was wrong. But I repeat now what I told them then: Shiran never got close enough for a point-blank shot.”

Manuel Pena ignored this evidence and argued that Sirhan Sirhan was a lone gunman. Shiran’s lead attorney, Grant Cooper, went along with this theory. As he explained to William Turner, “a conspiracy defence would make his client look like a contract killer”. Cooper’s main strategy was to portray his client as a lone-gunman in an attempt to spare Sirhan the death penalty by proving “diminished capacity”. Sirhan was convicted and sentenced before William W. Harper, an independent ballistics expert, proved that the bullets removed from Kennedy and newsman William Weisel, were fired from two different guns.

After Harper published his report, Joseph P. Busch, the Los Angeles District Attorney, announced he would look into the matter. Thane Eugene Cesar was interviewed and he admitted he pulled a gun but insisted it was a Rohm .38, not a .22 (the caliber of the bullets found in Kennedy). He also claimed that he got knocked down after the first shot and did not get the opportunity to fire his gun. The LAPD decided to believe Cesar rather than Donald Schulman, Karl Uecker and William W. Harper and the case was closed.

Cesar admitted that he did own a .22 H & R pistol. However, he claimed that he had sold the gun before the assassination to a man named Jim Yoder. William W. Turner tracked down Yoder in October, 1972. He still had the receipt for the H & R pistol. It was dated 6th September, 1968. Cesar therefore sold the pistol to Yoder three months after the assassination of Robert Kennedy.

Cesar had been employed by Ace Guard Service to protect Robert Kennedy at the Ambassador Hotel. This was not his full-time job. During the day he worked at the Lockheed Aircraft plant in Burbank. According to Lisa Pease, Cesar had formerly worked at the Hughes Aircraft Corporation. Lockheed and Hughes were two key companies in the Military-Industrial-Congressional Intelligence Complex.

Thane Eugene Cesar was a Cuban American who had registered to vote for George Wallace’s American Independent Party. Jim Yoder claimed that Cesar appeared to have no specific job at Lockheed and had “floating” assignments and often worked in off-limits areas which only special personnel had access to. According to Yoder, these areas were under the control of the CIA.

Yoder also gave Turner and Christian details about the selling of the gun. Although he did not mention the assassination of Robert Kennedy he did say “something about going to the assistance of an officer and firing his gun.” He added that “there might be a little problem over that.”

Lieutenant Pena was convinced that Sirhan Sirhan was a lone-gunman. He told Marilyn Barrett in an interview on 12th September, 1992: "Sirhan was a self-appointed assassin. He decided that Bobby Kennedy was no good, because he was helping the Jews. And he is going to kill him."He also added: "I did not come back (to the LAPD) as a sneak to be planted. The way they have written it, it sounds like I was brought back and put into the (Kennedy) case as a plant by the CIA, so that I could steer something around to a point where no one would discover a conspiracy. That's not so."