German coalition and opposition politicians can hardly conceal their restment as more details about the extent of the US National Security Agency's surveillance activities on private citizens are made public, including spy software for computers and mobile phones, mobile communication listening posts and manipulated USB ports. They don't necessarily agree, however, on how to tackle the scandal in Germany.

Early on, the opposition Left Party and the Greens demanded setting up a Bundestag investigative committee, regarded as the chamber's strongest weapon since, at least in theory, such a committee has the right to question an unlimited number of witnesses.

Presidential testimony?

The opposition parties, however, lack the 25 percent of the vote needed to appoint a Bundestag parliamentary inquiry on their own. Chancellor Angela Merkel's Christian Democrats (CDU) has more or less dismissed the idea, while the Social Democrats (SPD) have been hesitant.

Obama apologized to Merkel for the extent of the phone-monitoring

Surprisingly, Horst Seehofer, the head of the CDU's Bavarian sister party, the Christian Social Union (CSU), this week joined in the opposition's calls for an inquiry, even promising to help set up an investigative committee.

But Hans-Peter Uhl, a parliamentary spokesman on interior policy for the conservatives, says the CSU remains unconvinced whether such a committee makes sense, and he questions what exactly it would investigate. "A German parliament can't monitor the actions of foreign governments," Uhl told DW, noting that it is unclear who would be called to testify. It's not likely, he said, that "you'll get Obama as a witness before a German parliamentary inquiry."

Qualified witnesses

Hans-Christian Ströbele, a veteran Green Party lawmaker and member of the parliamentary committee that oversees German intelligence, disagrees. If German data transmitted via US-owned glass fibre cables or servers is no longer safe, he said, then "we can't just watch and say ‘that's a foreign intelligence service at work - we can't interfere.’" The problem of questioning qualified witnesses isn't new and is certainly no reason not to try, Ströbele told DW.

Berliners protested against NSA surveillance

SPD deputy Michael Hartmann remains unconvinced a committee would contribute much in clarifying NSA activities in Germany. NSA director Keith Alexander isn't likely to stop by in person, he told DW. The question is, he asked, “can an inquiry throw light on the issue, and if so, to what extent?"

Hartmann said the Social Democrats aren’t opposed to an inquiry, in principal, but it "should not be a shot in the dark or raise expectations it can't possibly fulfil." An inquiry, he added, should "confine itself to investigating to what extent Germany's intelligence agencies may be involved in the issue."

The SPD is in somewhat of a fix. When the NSA scandal surfaced in 2013, the party was still in the opposition and harshly critical of how Chancellor Merkel and her government handled the surveillance affair. Today, the SPD rules in a national coalition government with the CDU - and has had to adjust its tone of voice.

Snowden's role

The previous government, Hartmann concedes, kept a fairly low profile during the early days of the surveillance affair. But he says the situation changed when it became known that US intelligence wiretapped the Chancellor's cellphone.

Ströbele visited Snowden in Moscow in November 2013

Hartmann and Ströbele agree that former NSA contractor Edward Snowden, whose information triggered the scandal, would be a good witness for a potential parliamentary inquiry. Snowden, they say, may easily be the only one knowledgeable enough about the NSA - and willing - to testimony before a German committee.

Uhl has a different view of the NSA whistleblower, he believes Snowden was never an NSA expert. "He was an administrator who passed on data on a large scale but is in no position to assess the information he passed on," Uhl said.

But the dispute over Snowden, observers point out, is academic, even if a parliamentary inquiry were to begin its investigations into NSA activities in Germany. As the German government refuses to grant the NSA whistleblower political asylum, it is unclear how Snowden could testify before a committee in Germany without risking extradition to the US.