Washington (CNN) Special counsel Robert Mueller's investigators were allowed to review years of Michael Cohen's emails and other online data from the time he worked under Donald Trump, according to federal warrants released Tuesday.

The documents show that Cohen, Trump's former lawyer and fixer, was a target of Mueller almost immediately after the special counsel was appointed in May 2017 and how extensively Mueller tracked computer data of those close to then-candidate Trump in the early days of his presidency.

In all, prosecutors and the FBI received permission to execute four search warrants for Cohen's two Gmail accounts and stored data in his Apple iCloud account in July, August and November 2017 -- long before Cohen's office was raided in April 2018 and he pleaded guilty in an illegal campaign contribution and tax prosecution led by Manhattan federal prosecutors.

Mueller also received approval on two separate occasions to track the numbers of Cohen's incoming and outgoing calls.

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