WASHINGTON — In a bizarre twist, a federal agent who launched the investigation that ultimately led to the resignation of CIA chief David Petraeus was barred from taking part in the case over the summer due to superiors’ concerns that he was personally involved in scandal, The Wall Street Journal reported Tuesday.

After the discovery of allegedly inappropriate e-mails between General John Allen, the top commander in Afghanistan, and a Florida woman, US Defence Secretary Leon Panetta asked the Senate to put on hold the confirmation of Gen Allen. After being blocked from the case, the newspaper, citing officials, said the agent continued to press the matter, relaying his concerns to a member of Congress.

New details about how the FBI handled the case suggest that even as the bureau delved into Petraeus’s personal life, the agency had to address conduct by its own agent — who allegedly sent shirtless photos of himself to a woman involved in the case prior to the investigation.

FBI officials declined to identify the agent, so he couldn’t be reached to give his side of the story, the Journal said. The agent is now under investigation by the Office of Professional Responsibility, the internal-affairs arm of the FBI, according to two officials familiar with the matter.

The revelations address how the investigation first began and ultimately led to Petraeus’s downfall as director of the CIA. The new developments also raise questions about the role played by the FBI and the adequacy of notification to administration and congressional leaders about the scandal.

The FBI agent who started the case was a friend of Jill Kelley, the Florida woman who received harassing, anonymous emails that led to the probe, according to officials. Ms Kelley, a volunteer who organises social events for military personnel in the Tampa area, complained in May about the emails to a friend who is an FBI agent. That agent referred it to a cyber crimes unit, which opened an investigation.

However, supervisors soon became concerned that the initial agent might have grown obsessed with the matter, and prohibited him from any role in the investigation, according to the officials.

One official told WSJ the agent in question sent shirtless photos to Ms Kelley well before the email investigation began, and FBI officials only became aware of them sometime later. Eventually, supervisors told the agent he was to have nothing to do with the case, though he never had a formal role in the investigation, the official said.

A State Department official’s complaints about email stalking launched the months-long criminal inquiry that led to a woman romantically linked to former Gen David Petraeus and to his abrupt resignation Friday as CIA chief.

The agent, after being barred from the case, contacted a member of Congress, Washington Republican David Reichert, because he was concerned senior FBI officials were going to sweep the matter under the rug, the officials said. That information was relayed to top congressional officials, who notified FBI headquarters in Washington.

By that point, FBI agents had determined the harassing emails had been sent by Paula Broadwell, who had written a biography of Mr Petraeus’s military command.

Investigators had also determined that Ms Broadwell had been having an affair with Petraeus, and that the emails suggested Ms Broadwell was suspicious of Ms Kelley’s attention to Petraeus, officials said. The accusatory emails, according to officials, were sent anonymously to an account shared by Ms Kelley and her husband.

 Ms Broadwell allegedly used a variety of email addresses to send the harassing messages to Ms Kelley, officials said.