One connection between the soccer and dos Santos leaks is that each included the release of confidential documents from the powerful PLMJ law firm, which is based in Lisbon. Several of the charges Mr. Pinto faces in Portugal are directly linked to his illegally gaining access to PLMJ’s computer server.

It was lawyers from PLMJ who in 2015 prepared a 16-page brief for Ms. dos Santos pointing out the tax advantages of domiciling companies in Malta. Ms. dos Santos subsequently used companies based in Malta for some of her most high-profile transactions. One of her Maltese companies was used as a middleman to hire consultants from firms such as Boston Consulting Group, McKinsey & Company and PwC for advice on overhauling Angola’s state oil company, where she served as chairwoman from 2016 to 2017, after being appointed to the post by her father.

“We have of course no knowledge of the source of the documentation on which the recent press stories are based,” said Luís Pais Antunes, a managing partner at PLMJ. In any case, he added, “It is impossible that the documentation that is being used for the bulk of the stories is in any way related to PLMJ or was ever at our disposal.”

Unsure of exactly what he had when his soccer hacking turned up hundreds of thousands of pages related to the companies controlled by Ms. dos Santos and her husband, Mr. Pinto asked Mr. Bourdon, according to the French lawyer, if he could take a hard drive containing the data to a whistle-blower platform Mr. Bourdon had set up in Africa.

Mr. Bourdon said in an interview in the past week that he quickly came to the conclusion that the scale and complexity of the information meant it needed to be shared with the more experienced and better resourced International Consortium of Investigative Journalists. In the past week, that consortium and international news media organizations, including The Times, published details of Ms. dos Santos’s business dealings.