More than three years of work went into the report presented by investigative committee chairman Patrick Sensburg to the Bundestag on Wednesday, but in the end, no one was happy with it.

The multi-party parliamentary investigation was sparked by the 2013 revelation by former National Security Agency contractor Edward Snowden that US intelligence services had kept allies under surveillance, even going so far as to eavesdrop on Chancellor Angela Merkel's mobile phone.

"It's not okay for friends to spy on one another," Merkel said in her most famous statement when the affair broke.

But investigators soon found out that Germany's foreign intelligence service, the BND, had cooperated with the NSA and also kept tabs on its allies, for instance, by using so-called selectors - search terms for dragnet surveillance. The investigation was soon expanded to include the question of whether the US had piloted drones used in combat from its bases in Germany - an accusation that was never proven, although the report found that the German government often "looked the other way."

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The committee's report contains a head-spinning plethora of minutiae about everything from the technical specifications or capabilities of drones to various national and international intelligence operations. But it rarely reaches clear conclusions about what, if anything, was done wrong by whom. That was - as the report admits - down to fighting between political parties.

"Unfortunately, despite the common conviction of all parliamentary groups about the necessity of the investigation when it began, there were substantial disagreements between the governing and opposition groups about the methodology and goals of the committee's work," the report read.

The report was published by the governing coalition of the conservative CDU-CSU and Social Democrats alone, after a row last week about a 450-page dissent written by the opposition Left Party and the Greens. The chairman of the committee refused to publish that document, claiming it revealed classified information, whereupon the Left and Greens refused to sign off on the final version of the report as a whole and were removed from the committee.

Read: German opposition criticizes BND's illegal espionage

A massive document of dissent

Although the report is critical of both the US and German governments on a number of topics, on the underlying question of whether the US essentially betrayed Germany's trust, it reaches many "surprisingly positive" conclusions.

For example, one such passage read: "The committee is of the opinion that despite all the difference concerning NSA spying in the past there is relatively large agreement about the rigor and establishment of intelligence service oversight by the parliaments in Germany and the US."

Opposition parties would like more oversight of the BND's actions

The opposition Left Party and Greens see the situation entirely differently. In a section that was included in the official report, the two parties make a series of extremely critical recommendations, including subjecting German intelligence services to increased external and parliamentary oversight, strengthening IT security and ending what they call "a secret war in, from and with Germany."

"Germany and facilities located in Germany are not permitted to play any role in drone warfare that violates international law," the opposition parties wrote. "The German government must immediately and forcefully insist that all actions of this sort cease and must monitor it."

"Unprecedented, unparliamentary behavior"

The opposition also criticizes the fact that Snowden, who currently lives in asylum in Russia, was never able to testify in front of the committee because the German government refused to guarantee him safe conduct. In a TV interview on Wednesday morning ahead of the Bundestag debate, Green parliamentarian Konstantin von Notz called Snowden's absence "a damning indictment."

The Left Party and the Greens say they are evaluating whether to legally challenge what Notz called the governing coalition's "unprecedented un-parliamentary behavior."

The committee only succeeded in "scraping free" a part of the "surveillance infrastructure," Notz complained to the Tagesspiegel newspaper.

Opposition committee members like Notz heavily criticized the findings

Members of the governing parties disagree with that assessment and accuse the opposition of trying to create a scandal in an election year.

"There are no indications that Germans were spied upon en masse," conservative committee chairman Sensburg that newspaper.

The Social Democrats' lead figure on the committee, Christian Flisek, accused the opposition of a "complete refusal" to cooperate. But he also aimed a barb at conservatives and Merkel.

"There was a system of the very top of the Chancellery of not wanting to know anything," Flisek told dpa news agency.