The head of the Office for the Protection of the Constitution (BfV), Hans-Georg Maassen, said that the body maintained all security standards and had no way of knowing that a 51-year-old employee, hired last April, was a follower of the radical Salafist movement.

"We carried out a thorough background check in which we interviewed five references and looked at the entire spectrum [of information]," Maassen told reporters. "He was the father of a large family from a solid economic background who did good work. He apparently radicalized himself."

According to news magazine "Der Spiegel," the man, who was tasked by the BfV with observing the Salafist scene, had himself converted to Salafism in 2014 unbeknownst to the Office or even to his own family. He was uncovered after another BfV employee found him revealing confidential information on an Internet chat room and offering to help get a radical Islamist into BfV headquarters in Cologne, ostensibly for the purposes of a terror attack.

The 51-year-old, a German citizen who was born in Spain, was taken into custody on November 17, and the prosecutor's office in Düsseldorf says he has given a partial confession. His job at the BfV was his first job in the intelligence sector.

How could Germany's domestic intelligence agency employ an Islamist? And what if anything needs to change because of this case? The answers differ depending upon whom you ask.

An effective filter?

The BfV and the interior ministry deny that the man did any real damage to Germany's domestic security. And they say that the fact he was uncovered relatively quickly proves that established procedures are working.

"Of course, we'll thoroughly go through this case to see what we can learn from it," Maassen said. "In the course of our employment selection process, we've filtered out a whole series of people we think may be extremists and employees of foreign intelligence services."

The BfV has had to fill almost 500 new positions this year. Back in February, the Office told German public broadcaster ARD that checks against a database had revealed two right-wing extremists, a radical leftist, an Islamist and an employee of the Russian intelligence service among the applicants for a higher-level job.

German Interior Minister Thomas de Maziere of the conservative Christian Democrats (CDU) said the BfV had "performed well" in uncovering the Islamist. And a ministry representative offered reassurances that existing security vetting procedures were adequate.

"At the moment, we have no indications that there are fundamental structural problems," interior minister spokesman Tobias Plate said in Berlin on Wednesday. "On the contrary, the office itself was involved in uncovering this person."

Plate dismissed the idea that the suspect may have been just doing his job for the BfV - observing the Salafist scene - when he posted the messages in question on the chat room. And Plate also suggested that the "mole" was probably an anomaly.

"I can't remember any other recent cases that would be comparable at all with this one," Plate said. "It's certainly a special case."

How could it have happened?

Representatives of the center-left Social Democrats (SPD), junior coalition partners to the CDU, and Germany's opposition don't accept the depiction of the case as a one-off.

"The point is to know how the uncovered employee could have been hired in the first place despite background checks," SPD domestic security expert Burkhard Lischka told the DPA news agency.

Opposition spokespeople were far harsher in their criticism.

"What disturbs me is that the suspect only came to our attention by accident," the parliamentary vice-leader of the Green Party, Konstantin von Notz, told the "Handelsblatt" newspaper.

"The domestic intelligence service doesn't have a security leak - it is a security leak," the domestic policy spokeswoman of the Left Party, Ulla Jelpke, told the "Neue Osnabrücker Zeitung" newspaper.

So how easy or difficult is it to get a job at the Office for the Protection of the Constitution?

Help wanted

Applicants for jobs at the BfV are subject to the highest level of background checks allowed under German law. Candidates are required to provide a broad spectrum of information about themselves and their immediate families, including any past trouble with the law and contact to foreign intelligence agencies and groups hostile to the German constitution.

The BfV checks not only the accuracy of this information but interviews references provided by the applicant and other people deemed to have knowledge of the candidate. The test is repeated after five years. According to the BfV homepage, job candidates should not have prior legal convictions and should live in "orderly economic conditions."

Applicants are encouraged to show "discretion" in discussing their applications with others. The review process takes "several months."

The Düsseldorf prosecutor's office continues to investigate the case of the Islamic mole. Only when that process is concluded will the BfV, the interior ministry and Germany's political parties be able to determine whether background checks at the country's domestic intelligence service truly are rigorous enough.