The Department of Homeland Security's (DHS) inspector general "declined" to investigate the conduct of the Border Patrol agents who were pictured in September on horseback turning away Haitian migrants, and who were falsely accused by President Biden and some lawmakers of whipping migrants. 

The DHS announced Tuesday that U.S. Customs and Border Protection (CBP) initially referred the investigation to the Office of Inspector General (OIG), but that the OIG declined to investigate and referred the matter back to CBP’s Office of Professional Responsibility (OPR), which is the office charged with investigating alleged misconduct of CBP employees. 

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U.S. Customs and Border Protection mounted officers attempt to contain migrants as they cross the Rio Grande from Ciudad Acuña, Mexico, into Del Rio, Texas, Sunday, Sept. 19, 2021. (AP Photo/Felix Marquez)

The OPR is currently reviewing videos and photographs, as well as interviewing witnesses, employees, and CBP leadership in relation to the Sept. 19 incident in Del Rio, Texas, where agents on horseback were photographed blocking Haitian migrants from entering the U.S., and in one case grabbing onto a migrant’s shirt near the International Bridge. 

The photos sparked a firestorm and some media outlets and Democrats, including Biden, misidentified the agents’ split reins, which they use to control the horse, as "whips" and accused the agents of whipping the migrants. The photographer who took the images, meanwhile, said that he did not see anyone whip anyone either.

"To see people treated like they did, horses barely running over, people being strapped – it's outrageous," Biden said on Sept. 24, making a whipping motion with his hand. "I promise you, those people will pay. There will be an investigation underway now and there will be consequences. There will be consequences."

United States Border Patrol agents on horseback tries to stop Haitian migrants from entering an encampment on the banks of the Rio Grande near the Acuna Del Rio International Bridge in Del Rio, Texas on September 19, 2021. - The United States said Saturday it would ramp up deportation flights for thousands of migrants who flooded into the Texas border city of Del Rio, as authorities scramble to alleviate a burgeoning crisis for President Joe Biden's administration. (Photo by PAUL RATJE / AFP) (Photo by PAUL RATJE/AFP via Getty Images) (PAUL RATJE/AFP via Getty Images)

"What I saw depicted about those individuals on horseback treating human beings the way they were, was horrible," Vice President Kamala Harris told reporters on Sept. 21. "And I fully support what is happening right now, which is a thorough investigation into exactly what is going on there. But human beings should never be treated that way. And I'm deeply troubled about it. And I'll also be talking to [DHS] Secretary [Alejandro] Mayorkas about it today."

Once the OPR completes its investigation, the results will be provided to CBP management to determine whether disciplinary action is appropriate and, if so, the specific discipline to be imposed, the DHS said Tuesday.

The news came just hours before Mayorkas is set to appear before the Senate Judiciary Committee, where he will likely face questions about what he and the DHS are doing with the record numbers of migrants crossing the southern border.

Secretary of Homeland Security Alejandro Mayorkas on Oct. 8, 2021 in Mexico City, Mexico.  (Hector Vivas/Getty Images)

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Mayorkas said in September that the investigation of the agents on horseback would "be completed in days, if not weeks."

Mayorkas had initially backed the agents alongside Border Patrol Chief Raul Ortiz, noting the use of reins to control the horse. He later claimed he had not seen the images when he made those remarks and, while staying away from the "whip" claims, continued to call the images disturbing as the agents were placed on desk duty and the use of horses were ended in the Del Rio Sector.

Fox News’ Adam Shaw contributed to this report.