WASHINGTON — The person who gave the Panama Papers to reporters offered the first detailed explanation of the motive behind the largest leak of financial data ever.

In an 1,800-word statement, the leaker, identified by journalists as “John Doe,” assailed the world of offshore companies as fueled by “massive, pervasive corruption.”

“Shell companies are often associated with the crime of tax evasion, but the Panama Papers show beyond a shadow of a doubt that although shell companies are not illegal by definition, they are used to carry out a wide array of serious crimes,” the leaker wrote.

The person – whose identity has been kept under wraps since the leak was made public April 3 – called on authorities worldwide to investigate the Panamanian law firm of Mossack Fonseca and offered to help in the effort.

The source accused authorities, including those in the United States, of being “spineless,” said they were too conflicted by political interests to take action in the past, and said offshore activity has contributed to income disparity.

“For 50 years, executive, legislative and judicial branches around the globe have utterly failed to address the metastasizing tax havens spotting Earth’s surface,” the statement said. “Banks, financial regulators and tax authorities have failed. Decisions have been made that have spared the wealthy while focusing instead on reining in middle- and low-income citizens.”

The source has not been identified by Sueddeutsche Zeitung, the Munich, Germany, newspaper that first received the data, because the person expressed fear of retaliation. Sueddeutsche Zeitung shared the data with the Washington-based International Consortium of Investigative Journalists, which in turn cobbled together a team of more than 350 journalists in 78 countries, including several from McClatchy, to examine the 11.5 million documents. It was the largest media collaboration ever undertaken.

Sueddeutsche Zeitung verified the authenticity of the statement and shared it with its partners for release Friday.

“I am very sure this was handed over from the same person,” wrote Bastian Obermayer, the Sueddeutsche Zeitung reporter who received the leak. “We have certain mechanisms to verify who is on the other end … This is the person who contacted me.”

The statement shed little light on the leaker’s identity, but denied any connections between the leaker and any government. The website WikiLeaks has speculated that the source is connected to the U.S. government, but in Friday’s statement, the source indicated that he or she had attempted to contact WikiLeaks with the information.