WASHINGTON (AP) — House Republicans on Wednesday began their promised aggressive oversight of the Biden administration, focusing on what watchdogs described as "indications of widespread fraud" in federal coronavirus aid programs initiated under President Donald Trump.

GOP lawmakers complained that too little attention was paid to the problems when Democrats controlled Congress. Democrats blamed the Trump administration for much of the mess.

More than 1,000 people have pleaded guilty or have been convicted on federal charges of defrauding the myriad COVID-19 relief programs that Congress established in the early days of the pandemic. More than 600 other people and entities face federal fraud charges.

But that's just the start, according to investigators who testified as the House Oversight and Accountability Committee held its first hearing in the new Congress on fraud and waste in federal pandemic spending. Congress approved about $4.6 trillion in spending from six coronavirus relief laws, beginning in March 2020, when Trump was in the White House.

"We owe it to the American people to get to the bottom of the greatest theft of American taxpayer dollars in history," said Rep. James Comer, R-Ky., the committee chairman.

Gene L. Dodaro, head of the Government Accountability Office, told lawmakers that it will be some time before the full extent of fraud is known. The inspector general for the Small Business Administration has more than 500 ongoing investigations involving loan programs designed to help businesses meet operating expenses during the pandemic. The Labor Department's internal watchdog continues to open at least 100 unemployment insurance fraud investigations each week.

The GAO said the more than 1,000 convictions related to COVID-19 relief fraud are one measure of how extensive it was. "There are definitely indications of widespread fraud, but it's impossible to estimate right now what the full extent will be," Dodaro said.

The GAO reported in December that an extrapolation of Labor Department data would suggest more than $60 billion in fraudulent unemployment insurance payments during the pandemic in just that one program. The GAO also warned that such an extrapolation has inherent limitations and should be interpreted with caution.

Still, lawmakers are anxious to understand how much theft has occurred and what can be done to stop it in future emergencies.

"We must identify where this money went, how much ended up in the hands of fraudsters or ineligible participants, and what should be done to ensure it never happens again," Comer said.

Some 20 inspectors general work collaboratively to investigate pandemic relief spending. Michael Horowitz, who chairs a committee Congress created in March 2020 to lead oversight of COVID-19 spending, said data analysis is critical to detecting fraud.

For example, this week the committee issued a fraud alert regarding the use of questionable Social Security numbers to obtain $5.4 billion in pandemic-related loans and grants. He said a team of data scientist compared tens of millions of applications with data at the Social Security Administration to see if they fully matched the SSA's records.

"Over 69,000 didn't," said Horowitz, who also serves as the inspector general at the Justice Department. "This type of advanced data analytics is transforming how we do oversight."

One of the biggest factors in the COVID fraud that occurred was the need to get dollars out to people and businesses as quickly as possible. Horowitz said it is critical that agencies assess applicant eligibility before payments are sent out, but the Small Business Administration allowed entities applying for Paycheck Protection Program to self-certify they were eligible. He said that resulted in $3.6 billion going out to some 57,000 applicants on the federal government's do-not pay list, "a list the SBA did not bother to cross-check."

The House committee, which plans to examine an array of hot-button issues, includes some of the most strident critics of the Biden administration as well as some of its most ardent supporters. The clash in perspectives was evident from the start as Comer complained that the Biden administration faced little to no scrutiny last Congress.

"This committee has for too long stood on the sidelines while taxpayer dollars were wasted by bureaucrats whose only priority is getting money out the door," Comer said.

Rep. Jamie Raskin, the ranking Democrat on the committee, said the COVID relief programs "were by no means perfect." But he said the result of the programs was the shortest economic recession on record.

He blamed the Trump administration for allowing much of the fraud to occur. He said organized criminals and fraudsters took advantage of the overwhelming crush in demand for assistance and the problem was compounded by decisions "that hamstrung" the government's oversight.

"The Trump administration regularly told agencies to ignore data reporting requirements," Raskin said.

Horowitz said three programs that received about $2 trillion in funding account for most of the fraud that occurred: two loan programs designed to help small businesses and the unemployment insurance programs administered by the states.