The commission's findings have been supported by some writers but also challenged by various critics who hypothesize that Ruby was part of a conspiracy surrounding the Kennedy assassination.

He sold horse-racing tip sheets and various novelties, then acted as a business agent for a local refuse collectors union that later became part of the International Brotherhood of Teamsters (IBT).

[7] His sister, Eva Grant, said that he acquired the nickname because he resembled a slow-moving horse named "Spark Plug" or "Sparky" in the contemporary comic strip Barney Google.

He developed close ties to many Dallas police officers who frequented his nightclubs, where he provided them with free liquor, prostitutes, and other favors.

[14] An FBI report in 1956 stated that informant Eileen Curry had moved to Dallas with her boyfriend James Breen after jumping bail on narcotics charges.

[18] Stories of Ruby's eccentric and unstable behavior describe him as sometimes taking his shirt or other clothes off in social gatherings, and either hitting his chest like a gorilla or rolling around on the floor.

[11] During the 1970s, prominent psychiatrist Irene Jakab, who was known for her use of art therapy in diagnosing and treating patients with mental illness, analyzed artwork that had been created by Ruby while he was in jail.

While assessing one of Ruby's drawings, which had been included as part of art exhibits at the World Congress of Psychiatry meeting in Waikiki and the University of Hawaii in late August and early September 1977, she claimed that his work conveyed "repressed aggression and secretiveness," adding:[19] Notice how he really constricts himself so as not to reveal himself.

[20]: 336–337 John Newnam, an employee at the newspaper's advertisement department, testified that Ruby became upset over an anti-Kennedy ad published in the Morning News that was signed by "The American Fact-Finding Committee, Bernard Weissman, Chairman."

Early the next morning, Ruby noticed a political billboard featuring the text "IMPEACH EARL WARREN" in block letters.

In 1964, Robert H. Jackson of the Dallas Times Herald was awarded the Pulitzer Prize for Photography for his image, titled Jack Ruby Shoots Lee Harvey Oswald.

[citation needed] The grief over the assassination, Ruby stated, finally "reached the point of insanity," suddenly compelling him to shoot when Oswald walked in front of him in the basement that Sunday morning.

"[43][44] Ruby's brother Earl replaced Howard with prominent San Francisco defense attorney Melvin Belli, who agreed to represent him pro bono.

At his bond hearing in January 1964, while talking to reporters, Ruby tearfully said, regarding the assassination of Kennedy, that he could not understand "how a great man like that could be lost.

In June 1964, Chief Justice Earl Warren, Representative (and future President) Gerald R. Ford of Michigan, and other commission members went to Dallas to see Ruby.

[citation needed] Ruby asked Warren several times to take him to Washington D.C., saying that "my life is in danger here" and that he wanted an opportunity to make additional statements.

He added that the people from whom he felt himself to be in danger were the John Birch Society of Dallas, including Edwin Walker, who he claimed were trying to falsely implicate him as being involved in a conspiracy to assassinate the President.

"[41]: 194  Warren told Ruby that he would be unable to comply with his request because many legal barriers would need to be overcome, and public interest in the situation would be too heavy.

Arrangements were underway for a new trial to be held in February 1967[50] in Wichita Falls, Texas, but Ruby was admitted to Parkland Hospital on December 9, 1966, suffering from pneumonia, where he was diagnosed with cancer in his liver, lungs, and brain.

Footage that showed Oswald glance briefly in Ruby's direction as he emerged to shoot him, thought by some to be a look of recognition, compounded such suspicion.

Ruby drove into town with his pet dachshund Sheba to send an emergency money order at the Western Union on Main Street to one of his employees.

[43]: 18 The House Select Committee on Assassinations wrote in its 1979 Final Report: Ruby's shooting of Oswald was not a spontaneous act, in that it involved at least some premeditation.

There is also evidence that the Dallas Police Department withheld relevant information from the Warren Commission concerning Ruby's entry to the scene of the Oswald transfer.

[85] In his Warren Commission testimony, Detective Don Archer claimed that, after his arrest, Ruby looked him straight in the eye and said, "Well, I intended to shoot him three times."

[97] Not long before Ruby died, according to an article in the London Sunday Times, he told psychiatrist Werner Teuter that the assassination was "an act of overthrowing the government" and that he knew "who had President Kennedy killed".

Scheim cited in particular a 25-fold increase in the number of out-of-state telephone calls from Jack Ruby to associates of these crime bosses in the months before the assassination.

[104] According to author Vincent Bugliosi, both the Warren Commission and the House Select Committee on Assassinations determined that all of these calls were related to Ruby seeking help from the American Guild of Variety Artists in a matter concerning two of his competitors.

[105] The House Select Committee on Assassinations report stated that "most of Ruby's phone calls during late 1963 were related to his labor troubles.

[108][109] The House Select Committee on Assassinations undertook a similar investigation of Ruby in 1979, 15 years after the written report, and said that he "had a significant number of associations and direct and indirect contacts with underworld figures" and "the Dallas criminal element," but that he was not a member of organized crime.

[110] In a memo dated to the day of Oswald's murder J. Edgar Hoover, Director of the FBI, wrote that "We have no information on Ruby that is firm, although there are some rumors of underworld activity in Chicago".