The investigation was prompted by reports of a relationship between Ms Hill and a member of her congressional staff, which she denied.

The news was met with an apparent takeover of Ms Hill's government Twitter account, with anonymous posts accusing the Democrat of abuse.

"Katie Hill is not a hero for women," the post said, written by someone claiming to be her former staff.

Ms Hill has denied wrongdoing in relation to the post, and reported the "hacking" of her account.

Control of the Twitter account, previously reserved for Ms Hill's congressional work, was handed over to House officials upon her resignation, Ms Hill said. "God knows who hacked it from there."

Who is Katie Hill?
The 33-year-old Democrat was once seen as a rising star in the party. Elected in 2018 as part of a Democratic wave, Ms Hill beat a Republican incumbent in California's 25th Congressional district.

The freshman lawmaker joined a congressional class that boasted a record-breaking number of women. Ms Hill was also one of the first openly bisexual people to serve in Congress.

But her promising political career was cut short last year, when a convoluted ethics scandal prompted her resignation.

Allegations first emerged on the conservative blog RedState, which claimed Ms Hill and her then-husband, Kenny Heslep, had engaged in a sexual relationship with a woman in her twenties who had worked on Ms Hill's congressional campaign.

In a letter to constituents, Ms Hill apologised for the affair, writing that "even a consensual relationship with a subordinate is inappropriate".

"But the truth is, distributing intimate photos with the intent to publish is a crime," she said at the time, referring to Washington's 2014 "revenge porn" law, and directed the matter to Capitol Police.

Ms Hill levelled blame at Mr Heslep, who she described as "an abusive husband who seems determined to try to humiliate me".

He is reported to have denied the accusations and claimed his computer had been hacked.