The case involved a Slovene central bank decision to cancel part of NLB’s debt, held in the form of subordinated bonds.

The central bank issued the “urgent measure” on grounds that NLB was at risk due to its negative working capital - a situation in which a bank’s current liabilities exceed its monetizable assets - resulting in the multi-million euro windfall.

The Slovenian National Investigation Bureau started its pre-trial investigation in December 2014 after police received several accusations of foul play.

The criminal inquiry is being led by the Special Prosecutor's Office for organised crime, corruption and terrorism.

For its part, the Central Bank of Slovenia confirmed on Wednesday that individual employees’ homes had been searched in connection with a pre-trial probe.

It said it could not give further information due to the ongoing nature of proceedings. But its press release added links to a letter of complaint by Mario Draghi, the head of the European Central Bank (ECB).

Draghi’s letter, which was addressed to the European Commission and to Slovenia’s prosecutor general, said the police was guilty of “unlawful seizure of ECB information” and of violating “the ECB’s privilege on inviolability of its archives”.

He said the raids could stop the Slovenian central bank from doing its job as part of the eurozone governance system and could impede the governor, Jazbec, from fulfilling his tasks as one of the ECB’s managers.

The Slovene police said on Thursday that central bank employees do not enjoy special immunity and that they performed the raids in line with a search warrant.

A commission spokesman in Brussels said it is “too early” to comment on the “ongoing” proceedings.

The case dates back to autumn 2013, when Slovenia injected more than €4.5 billion into its banks on the back of stress tests conducted by international consultancy firms Ronald Berger and Oliver Wyman.

The bailout stirred controversy because thousands of bank bond holders were subjected to haircuts that wiped out their investments overnight.

Many of them filed complaints, criminal charges and libel suits against bank authorities.

One of the cases went all the way to the European Court of Justice (ECJ) after Slovenia’s constitutional court referred it to the EU tribunal for clarification.

According to criminal charges filed by the Panslovenian Shareholders Association, NLB had surplus capital of €835 million as of 30 September 2013.

But the same day, Jazbec’s central bank said NLB had negative capital of €318 million and imposed the haircut on holders of subordinated bonds - financial instruments with a lower guarantee of pay-back if the issuer gets into trouble.

The Panslovenian Shareholders Association said that if the Central Bank of Slovenia was telling the truth, then NLB falsified its balance sheets to the tune of more than €1 billion.

It says that if the NLB balance sheet was really in the red, then NLB still failed to protect its investors’ assets and its people should still face criminal charges.

The pain of the 2013 bank overhaul was felt directly by some in the country.

In January 2014, the general manager of Bank of Celje committed suicide after the central bank renationalised the lender and imposed haircuts.

Under the Slovene criminal code, a person guilty of abuse of office or official duties who has acquired for himself or a third person a large financial benefit that corresponds to his initial intent should go to jail for between one and eight years.