A new report sheds light on why longtime FBI investigator Peter Strzok was removed from special counsel Robert Mueller's investigation into Russian interference in the 2016 election and possible collusion between the Trump campaign and the Kremlin.

Sources told the New York Times that Strzok had come under investigation by the Justice Department's inspector general after the discovery of texts he sent to a colleague that could be construed as being anti-Trump. He had been reacting to events in the news, like the presidential debates.

After being removed from the Mueller probe over the summer, Strzok was shifted to the FBI's human resources department.

Strzok's lawyer did not comment for the Times report, while a Justice Department spokeswoman said those within the agency are "aware of the allegation and are taking any and all appropriate steps.”

The exact content of the texts have not been disclosed, but whom he was texting was later revealed in a follow-up report, which also added further concerns of problematic behavior by Strzok. The Washington Post reported that Strzok had been texting FBI lawyer Lisa Page, who worked for Deputy Director Andrew McCabe and had been part of the Mueller team into the summer.

The two had also been involved in an extramarital affair during the FBI's Hillary Clinton email investigation, which Strzok had been working on.

A spokesperson for Mueller put out statement addressing both Strzok and Page.

“Immediately upon learning of the allegations, the Special Counsel’s Office removed Peter Strzok from the investigation. Lisa Page completed her brief detail and had returned to the FBI weeks before our office was aware of the allegations," the statement read.

Strzok's departure was previously reported in August by ABC News, but the motivation behind the move was unclear at the time.

Strzok previously led the FBI's counter-espionage section.

The reports come one day after former National Security Advisor Michael Flynn pleaded guilty to lying to the FBI in January about his contacts with the Russian ambassador.

Flynn was charged on one count of “willfully and knowingly” making “false, fictitious and fraudulent statements” to the FBI about communications exchanged with then-Russian Ambassador Sergey Kislyak shortly after Trump took office.