Julius and Ethel Rosenberg (nee Ethel Greenglass) in a Marshal's van en route to the Federal House of Detention, after they had been found guilty of nuclear espionage. They were subsequently executed.  (Photo by Keystone/Getty Images)
Washington CNN  — 

The sons of Ethel and Julius Rosenberg, two convicted communist spies who were sentenced to death during the Cold War, visited the White House without an invitation on Thursday to call on President Barack Obama to exonerate their mother, in what they see as their final shot.

Robert and Michael Meeropol have been advocating on behalf of their parents for over 63 years since they were convicted of providing secrets of the atomic bomb to the Soviet Union and executed by electric chair.

In recent years, court documents and witnesses have cast doubt on what crimes the Rosenbergs actually committed or what role Ethel Rosenberg played.

Ethel Rosenberg’s brother, David Greenglass, told investigators at the time that he saw Ethel typing up information on the Atomic Bomb that he received while working on the Manhattan Project. But in 1950 grand jury testimony released last year, Greenglass said he never spoke about the information on the atomic bomb with his sister, only her husband and his own wife.

The brothers, who brought with them to the White House a package of information for Obama on their mother’s case and a petition with over 40,000 signatures, were advocating for the President to exonerate their mother before leaving office.

The Meeropol attempted to deliver the papers to the front gate of the White House, speaking to Secret Service through an intercom but were turned away due to protocol. “Well, we tried,” Michael Meeropol said adding that they had sent copies to Valerie Jarrett, senior adviser to Obama.

Press Secretary Josh Earnest provided little hope for the brothers in the White House briefing Thursday saying, “I think it’s fair to say that any action on this matter before the end of this presidency is unlikely.”

Earnest said that he was not aware of any work that has started on their request but added “I’m sure we’ll take a look.”

“Since we can’t bring her back to life, there would be nothing more satisfying to us then to have the government acknowledge that this shouldn’t have happened.” Robert Meeropol said outside the White House Thursday.

The brothers have little hope that their mother would be exonerated by President-elect Donald Trump because they say one of the “principle architects” behind their mother’s case was Roy Cohn, who was once Trump’s attorney.

Robert Meeropol said the chances of Trump doing anything to help his mother’s case strikes him as “nil.”

“Therefore this is the time to do it. If we don’t get Obama to do it we are virtually certain that Trump will not,” he said.

Michael Meeropol also stressed that his parent’s trial is a “cautionary tale” saying the United States is in danger of another period of “hysteria” and “targeting people,” which is similar to what their parents faced during the Cold War.

The brothers said they were not pursuing exoneration for their father because while they claim he was framed for stealing information of the atom bomb, they do acknowledge that he was guilty of espionage.

In 1997 an aging former KGB agent who had direct contact with Julius and Ethel Rosenberg said the American couple were executed unjustly because they never provided Moscow with any useful material about the atomic bomb, The New York Times reported at the time.

Alexander Feklisov told the Times that Rosenberg had provided him with military secrets but had never handed over anything of substance about the atomic bomb. The two men met frequently between 1943 and 1946, he said.

CNN’s Tim Garraty contributed to this report