Israeli prime ministers from Ehud Barak to Benjamin Netanyahu have personally lobbied US presidents for his release. Bill Clinton, George W. Bush and Barack Obama all declined the requests.

Jonathan Pollard was sentenced in 1987 to life in prison for smuggling more than 1,000 classified US documents to Israel, amounting to tens of thousands of pages. The former civilian intelligence analyst for the US Navy was released on parole Friday after serving 30 years behind bars.

Pollard's case has been a long-standing sore spot between the two allies. Caspar Weinberger, secretary defense at the time of Pollard's arrest, accused him of causing "the greatest harm to our national security." That claim has been disputed by other US government officials.

After initially denying that Pollard had spied for them, Israeli officials subsequently apologized and claimed a renegade intelligence unit was responsible for the espionage. Pollard was granted Israeli citizenship in 1995.

"The person who was the head of that intelligence unit, Rafael Eitan, told me that he received authorization from higher ups," Eytan Gilboa, an expert on US-Israeli relations who has closely followed the Pollard case, told DW.

"I don't know if this is true or not. Shimon Peres denied that," Gilboa said, referring to the former prime minister and president of Israel.

What did Pollard steal?

Pollard has claimed he sought to protect Israel, not to hurt America. Washington, at the time, was withholding important information from Israel that was key to its national security, Pollard said during his trial.

"It was my plan to provide such information on the Arab powers and the Soviets that would permit the Israelis to avoid a repetition of the [1973] Yom Kippur War, in which they were confronted with nothing less than a technological Pearl Harbor," Pollard wrote in a 1987 pre-sentencing statement.

According to the "Washington Post," Pollard handed Israel classified US intelligence on Libyan air defenses as well as French and Russian naval movements in the Mediterranean. This allowed Israeli warplanes to avoid detection and blow up the Palestinian Liberation Organization's headquarters in Tunis in 1985. He also passed information to Israel on Iraq's and Syria's chemical warfare programs as well as Pakistan's nuclear program.

"I was, quite literally, Israel's eyes and ears over an immense geographic area stretching from the Atlantic to the Indian Ocean," Pollard wrote in his statement.

Did Soviets receive intelligence?

Pollard's staunchest detractors have said he was motivated by greed. The Israelis paid him up to $2,500 a month and promised to deposit $300,000 in a Swiss bank account over 10 years.

It's been alleged that the information Pollard sold didn't remain in Israeli hands. "New Yorker" magazine reported in 1999 that the Israelis transferred US intelligence to Moscow, in exchange for Soviet Jews receiving exit visas.

"I'm not persuaded by that," Robert Freedman, an expert on US-Israel relations at the Strategic Studies Institute, told DW. "Gorbachev, for his own reasons, wanted to let the Soviet Jews out - to improve relations with the US."

Miscarriage of justice?

A growing number of American officials had called for Pollard's release. Thirty-nine Democratic members of Congress signed a 2010 letter to Obama requesting clemency for Pollard. The signatories said Pollard had served enough time for his crime, considering that he smuggled classified information to an ally, not an enemy.

There have also been allegations that his harsh sentence was the consequence of anti-Israeli sentiment in the US government at the time. Lawrence Korb, assistant secretary of defense when Pollard was arrested, also wrote a letter to Obama in 2010 calling for clemency.

"Based on my first-hand knowledge, I can say with confidence that the severity of Pollard's sentence is a result of an almost visceral dislike of Israel and the special place it occupies in our foreign policy on the part of my boss at the time, Secretary of Defense Caspar Weinberger," Korb wrote.

'Crisis of mistrust'

According to Freedman, political considerations didn't factor into Pollard's parole. Some observers have speculated that he was freed to ease tensions with Israel over the Iran nuclear deal. Pollard was eligible for parole after 30 years and the parole board simply decided in his favor, Freedman said.

The Obama administration has declined to give Pollard special treatment, for example, by intervening and allowing him to leave for Israel where his wife lives. As a condition of his parole, Pollard has to remain in the United States for five years. According to Gilboa, the Pollard case has not had a negative long-term impact on US-Israel relations.

"There was a crisis of mistrust between the intelligence services of Israel and the US for five years after the eruption of the case," Gilboa said. "The absurdity of the whole thing is after that, in the mid-1990s and especially after 9/11, there's been very close collaboration between Israeli and US intelligence services."