The Democrat who vacated the US House seat won by the controversial Republican George Santos said on Tuesday Congress was letting in “a con man”.

Tom Suozzi won New York’s third district, which covers parts of Long Island and Queens, in 2016, but stepped down in 2022 in order to run for governor. Santos lost to Suozzi in 2020 but beat Robert Zimmerman for the vacant seat.

Since Santos’s victory, almost every part of his campaign biography has been called into question.

Intense scrutiny has been applied to his claims about his education and career in business and to elements of his personal story, including his supposed descent from Holocaust survivors and a claim that his mother died as a result of the 9/11 attacks. Santos has admitted to some inaccuracies.

But even after prosecutors in Brazil reactivated a criminal fraud investigation regarding the use of a stolen chequebook, and amid reports that federal prosecutors in New York are examining Santos’s background and financial dealings, Republicans in Congress have not acted.

On Tuesday, as the new Congress gathered, Suozzi pointed out in a column for the New York Times that on being sworn in, Santos would take “an oath to ‘bear true faith’ to the constitution and [to] take this obligation without any ‘purpose of evasion’”.

Suozzi wrote: “I’ve lost track of how many evasions and lies Mr Santos has told about himself, his finances and his history and relationship with our stretch of Long Island and north-eastern Queens.”

Santos being seated in Congress, Suozzi said, would “diminish our Congress, our country and … his constituents.

“It saddens me that after 30 years of public service rooted in hard work and service to the people of this area, I’m being succeeded by a con man.”

When Santos arrived on Capitol Hill, he ignored questions from a scrum of reporters. Before being sworn in, he supported Kevin McCarthy for speaker. He could not be formally sworn in until the speakership had been decided. That process was delayed until Wednesday at least, an overnight adjournment having followed three inconclusive votes.

Suozzi said Santos could still be held to account by “our democracy, our free press and the rule of law” as well as “the voters of the third district”.

Those voters, he wrote, “believe in the rule of law, in playing by the rules. They like authenticity in their leaders and pride themselves on having a good BS detector.

“The fact is that Mr Santos’s behavior went beyond BS: he fabricated the basics of his biography to an extent that most voters wouldn’t have thought possible. The shame would be too great, right?”

Lamenting the rise of political shamelessness, Suozzi pointed to Donald Trump’s famous 2016 claim that “he could ‘shoot somebody’ on Fifth Avenue and still not lose supporters”.

Suozzi wrote: “If we are going to subdue the tyranny of unchecked liars and their lies then Mr Santos must be held accountable: he must be removed by Congress or by prosecutors, because there is no indication that he will be moved by conscience to voluntarily resign.”

Suozzi likened Santos to Sam Bankman-Fried and Bernie Madoff, the former a cryptocurrency magnate who has pleaded not guilty to charges of fraud, the latter sentenced to 150 years in 2009 over the largest Ponzi scheme in history.

Suozzi said: “Not unlike them, [Santos] appears to have conducted his finances in highly unusual, if not unlawful, ways. But I have to wonder, having seen his delight for attention and his self-regard, if he loves that everyone now knows his name – even though it’s because of yet another big lie.”

Suozzi insisted Santos would be held accountable.

“The people of my district are holding rallies, signing petitions and calling on the Republican leadership to act,” he wrote.

Calling the district “a model for moderation … a 50-50 district with constituents who embrace a get-it-done attitude” and “value tell-it-like-it-is leadership”, Suozzi said those voters now found themselves “saddled with a slippery, inexperienced liar who tells it like it isn’t”.

Such New Yorkers, Suozzi said, were now “counting on the press to keep digging in, law enforcement to keep investigating and the political pressure to keep building on the House”, in order to remove Santos from Congress.