LA Times: "Strzok initially helped lead the bureau's investigation into Russian interference in the 2016 election and possible complicity by the Trump campaign, which remained secret until after the election."
Washington Post: "The FBI has fired agent Peter Strzok, who helped lead the bureau's investigation of Russian interference in the 2016 presidential election until ..."
The Guardian: " FBI agent Peter Strzok, who once helped lead the bureau’s investigation into Russian election interference and sent texts disparaging Donald Trump, has been fired by the bureau."
NBC News: "Peter Strzok, the senior FBI official who helped lead the initial probe of ties between Russia and the Trump campaign until it was discovered he sent anti-Trump texts, was fired from the agency on Monday, NBC News has confirmed."
USA Today: "Strzok, who worked for the bureau for 22 years, helped lead the investigations into Russia's interference in the 2016 presidential election and into Hillary Clinton's use of a private email server while she was secretary of state."
VOX: "The FBI has fired Peter Strzok, a top agent who had investigated the Trump ... became the lead agent on the bureau's counterespionage team."
CNN: "Strzok played a lead role in the investigation into Hillary Clinton's private email server and was involved in the FBI's recommendation that no criminal charges be filed against the former secretary of state. He later helped oversee the beginnings of the probe into Russian meddling in the 2016 election, and his involvement in both investigations has been seized on by Republicans as evidence of anti-Trump bias in the bureau..."
Why would I say the he was the LEAD AGENT? It's pretty simple, he was.