According to media reports, the suspected BND double agent unmasked last week could have passed on secret information about the situation in Ukraine to Russia.
This was reported by NDR and WDR on Monday.
It was also said, citing information from security circles, that the officer may have been blackmailed.
According to the report, the Federal Public Prosecutor or the foreign intelligence service BND did not want to comment.
Both only referred to their press releases from last Thursday.
The BND employee Carsten L. was unmasked by the Federal Intelligence Service and, according to the authorities, was arrested on Wednesday last week on the instructions of the federal prosecutor.
He is accused of having passed on state secrets to a Russian secret service.
Nothing is known about his function within the BND.
It is also unclear how the BND found out about it.
The Federal Criminal Police Office searched the suspect's home and workplace and one other person.
The investigators are investigating whether Carsten L. had supporters or accomplices.
Treason (Article 94 of the Criminal Code) carries a prison sentence of at least one year and a maximum of 15 years, and in particularly serious cases it can even be life imprisonment.
The offense is the most serious of the crimes involving threats to external security.
Anyone who commits treason betrays a state secret to a foreign power.