Sebastian Edathy’s lawyer released a statement on the politician’s Facebook page which said investigators had “lost all sense of moderation” in his client’s case.
The 44-year-old was a rising star of the Social Democrats (SPD) until two weeks ago when he resigned, citing health reasons. But two days after he quit, his home and office were raided by police who suspected him of possessing inappropriate images of children.
Prosecutors said the case against Edathy involved naked pictures of boys aged nine to 14, but Edathy has denied the allegations.
The statement released by Edathy’s lawyer late on Monday said his client would start legal proceedings against prosecutors.
The lawyer said: “To the disregard of the presumption of innocence and the naming of private details will now be added the breach of official secrets.”
Edathy and his lawyer are annoyed that the Frankfurter Allgemeine Zeitung (FAZ) reported on Sunday details about films of naked children which Edathy allegedly ordered on the internet from Canada.
“Mr Edathy must assume that the investigating authorities have made the entire investigation file available to the Frankfurter Allgemeine Zeitung," the statement said. "This is a criminal offence. Investigators who themselves commit crimes, are seen unfit to lead a criminal case.”
His lawyer said the case against Edathy should now be dropped. The statement said searches against Edathy were being made in the “mere hope” of finding something.
But in a blow for the politician, the SPD said earlier on Monday it would start proceedings to throw Edathy out of the party.
"Formal proceedings have started against Mr Edathy," SPD general secretary Yasmin Fahimi said.
The Federal Office of Criminal Investigations (BKA) also came under heavy fire on Monday for its role in the scandal.
It claims it did not know Edathy's name had been on a list of suspected child pornography buyers for two years.
Politicians from Die Linke, Green and Free Democrat (FDP) parties all voiced disbelief that the BKA did not know.
“It is absolutely not plausible that information about Edathy did not reach the BKA ,” said Die Linke chief Bernd Riexinger.
FDP vice chairman Wolfgang Kubicki told the Bild newspaper that in the ranks of the BKA “either idiots were at work or they were trying to avoid a scandal”.
Even the Christian Social Union (CSU) – the Bavarian sister party of Chancellor Merkel's dominant CDU – expressed confusion.
Interior spokesman Stephan Mayer told the Bild: “It is inexplicable that the BKA did not notice that Edathy's name was on the list of child porn buyers."