Germany has paid millions of euros for the so-called Panama Papers revealing offshore tax evasion, reports say.
The Federal Crime Office (BKA) said it would put the multi-million-file inventory into electronic form to allow for detailed evaluation.
It did not confirm the sum, but government sources told German media 5m euros (£4.4m; $5.7m) had been paid.
The documents leaked last year exposed rich and powerful people, who had used tax havens to hide their wealth.
The leaks put heads of state, businessmen and celebrities under pressure, with some resigning over the revelations.
Months of investigation
Some of the approximately 11.5m documents from Panamanian law firm Mossack Fonseca were leaked initially to Germany's Süddeutsche Zeitung and then to other news organisations in co-operation with the International Consortium of Investigative Journalists.
Süddeutsche said it had refused to pass on the documents to protect its sources and reported that a team of federal police and prosecutors had travelled to Panama City last week to meet local officials. Police said that reviewing the data was likely to take several months.
While paying large sums for unlawfully obtained data has been ruled legal by Germany's constitutional court, it remains controversial.
When Denmark paid a smaller sum to buy data allegedly implicating up to 600 Danish citizens last September, opposition parties attacked the decision as "deeply reprehensible".
The Panama Papers leak was the biggest in history. Some of the documents have been published by various media organisations but many remain unpublished.
Germany, France and the UK are all believed to have paid for data on bank customers in the past in an attempt to crack down on tax evasion.
"These data are being looked into and evaluated with Hesse state's tax authorities to pursue criminal and fiscal offences," the BKA said in a joint statement (in German) with Hesse's finance ministry and the public prosecutor's office in Frankfurt.
As well as tax fraud, investigators will also be looking for evidence of arms trafficking and organised crime.
Panama Papers - tax havens of the rich and powerful exposed
BBC Panorama and UK newspaper The Guardian were among 107 media organisations in 76 countries which analysed the documents. The BBC does not know the identity of the source
- The documents show how the company helped clients launder money, dodge sanctions and evade tax
- Mossack Fonseca says it has operated beyond reproach for 40 years and never been accused or charged with criminal wrongdoing
- Read more: How assets are hidden and taxes evaded