Robert Mueller, the former FBI director and special counsel whose Russia investigation shadowed much of Donald Trump’s first presidency, has died at 81, his family said. The cause of death was not immediately disclosed.

Mueller, a decorated Vietnam veteran, led the FBI from 2001 to 2013. He returned to the national spotlight in 2017 when he was appointed special counsel to investigate Russian interference in the 2016 election and possible links to Trump’s campaign. Mueller’s investigation found that Russia had attempted to interfere in the 2016 election but could not conclude that there had been any attempt by Trump or his campaign to collude with Russia in the effort.

Trump, who long denounced the inquiry as a “witch hunt,” wrote on Truth Social on Saturday: “I’m glad he’s dead. He can no longer hurt innocent people!”