Mueller has searched the electronic devices of at least one Russian oligarch while probing illegal contributions to Trump

Special counsel Robert Mueller has begun questioning Russian oligarchs over whether they “illegally funneled cash donations directly or indirectly into Donald Trump’s campaign and inauguration”—and stopped at least one at a New York airport to search his electronic devices, CNN reports.

According to CNN, another “Russian oligarch was stopped during a recent trip to the U.S.,” and a third received an “informal voluntary document and interview request” from Mueller’s team.

In each situation, Mueller’s team has asked about the oligarchs’ donations to Trump’s campaign—which is prohibited under campaign finance laws.

The news comes after a Washington Post report, published Tuesday, that revealed Mueller has told Trump’s legal team that the president is not a “criminal target” of his probe—but remains a subject of the investigation.