The source confirmed reports in German media that the man had roles in those movies but added that the development did not appear to be related to the alleged terrorist plot.
The prosecutors' office in Duesseldorf said Wednesday it had opened a criminal investigation against the man, a 51-year-old German citizen, on suspicion of "preparing a serious violent act endangering the state."
He had worked for the German Federal Office for the Protection of the Constitution since April, it said. He was arrested November 16 over allegations of sharing protected materials and making Islamist statements online.
According to the statement from the prosecutors' office, the intelligence service employee "was tasked with the observation of the potentially violent Salafist scene" -- referring to an ultrafundmentalist branch of Islam.
"The investigation is based on the following points: suspicion of preparing a serious violent act endangering the State, the attempted violation of intelligence secrets and the readiness to commit a crime," it said.
"The suspect is accused as identifying himself as an intelligence employee in an internet chat and to have revealed accurate information of operations including content and locations."
Suspect uncovered by fellow spy
The man is also accused of offering his chat partner access to the domestic intelligence agency "to commit violent acts against 'non-believers' which 'were surely the wish of Allah' and that 'he was prepared to do anything to help his brothers,' " the prosecutors' office statement said.
However, the suspect's chat partner was an employee of the same intelligence agency and was able to uncover the man's identity, it said.
"The suspect -- who describes himself as a 'convert' -- has confessed his goal as infiltrating the domestic intelligence service and warning his 'brothers' of current investigations."
Further allegations may be made against the man once confiscated data storage has been examined, the statement said. This would determine whether the case is handed to the federal prosecutor.
"As of now, there is no evidence that the suspect managed to reveal any security-related secrets to people in the violent Salafist scene, or has committed any other crime," the statement said.
The case has raised questions over how the man, who has been in custody since November 17, came to be recruited to the intelligence agency in the first place.
"The security vetting of applicants needs to be examined," Social Democrat lawmaker Burkhard Lischka said.
Last month, German authorities banned an Islamist organization
they said was responsible for inspiring more than 140 young people to join the conflict in Syria.
Federal police in September said 800 German nationals had traveled to Syria to join the conflict.
German Chancellor Angela Merkel in July vowed to boost security and improve counterterrorism measures
following three attacks allegedly carried out by refugees. Merkel has come under criticism for her open-door refugee policy, which saw more than 1 million asylum seekers enter the country in 2015.
Germany has banned several Islamist associations in recent years, including ISIS in 2014 and the jihadist group Tauhid Germany in 2015.