The FBI is linking a hacker known by the name mr. grey to 1.2 billion stolen Internet credentials after identifying his Russian email address in the evidence it collected.

Citing FBI’s court documents, Reuters reported that the hacker was identified based on data from a cybsecurity company which in 2014 said that it had determined an alleged Russian crime ring was responsible for stealing information from over 420,000 websites.

In August last year, Hold Security revealed that a Russian hacking group gathered more than 1.2 billion user name and password combinations and over 500 million email addresses.

The documents said the FBI identified lists of domain names and utilities that investigators think were used for sending spam.

The FBI also found an email address registered in 2010 contained in the spam utilities for a mistergrey, the documents reveal.

The so-called mr.grey claimed to have access to large pools of user data acquired from Twitter, Facebook and Russian social network VK.