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Top officials failed to properly investigate allegations of a kickback and expense account fraud scheme by Border Patrol (search) agents in an inquiry that appeared to whitewash the potential involvement of higher ups, says a government watchdog agency.

The report sent to Congress and President Bush (search) by the U.S. Office of Special Counsel, an independent agency created to protect government whistleblowers, said later investigations by the Department of Homeland Security (search) also failed to hold high-level officials responsible.

"It stretches credulity that 45 employees at a single Border Patrol station engaged in a kickback and fraud scheme for a number of years ... without the knowledge of management," the OSC said in a statement released Tuesday that calls for further investigation.

It said Homeland Security investigators "appear to have exerted little effort to follow up on evidence identified by ÛBorder PatrolÝ whistleblowers that would call into question the statements of its management."

Internal investigations by the Justice and Homeland Security departments have found that high-level Border Patrol officials committed no wrongdoing and did not engage in any cover-up.

The OSC report said the current head of the Border Patrol, David V. Aguilar, was informed as early as 2000, when he headed the agency in Arizona, that border agents temporarily assigned there were receiving kickbacks from area landlords, but did not act.

Of the nearly 70 Border Patrol employees suspected of wrongdoing, 45 were punished in some fashion, although almost all were low-ranking agents.

By sidestepping punishment of higher-ups under suspicion, "there is a real risk of creating the appearance of a whitewash," Special Counsel Scott J. Bloch said in a statement.

The report involves allegations by whistleblowers Larry E. Davenport and Willie A. Forester, former Border Patrol Agents, that agents and at least 16 supervisors in Operation Safeguard were involved in kickback and fraudulent lodging reimbursement claims.

The OSC report says two high-ranking Border Patrol officials in the Tucson sector to whom the whistleblowers complained were Rowdy Adams and Carlos Carrillo, both of whom were personally close to Aguilar, then the head of the Border Patrol in that sector. Both followed Aguilar to Washington last summer when he became the Border Patrol's chief.

In Operation Safeguard, the Border Patrol dispatched more than 1,000 of its uniformed agents to Arizona for one- to three-month assignments to try to stem the flow of illegal immigrants across the border.

Many of the recently hired agents were on their first out-of-town deployment.

Adams now is a Border Patrol senior associate chief who oversees technology issues, such as its multibillion-dollar America's Shield Initiative to place cameras and sensors along U.S. borders. Carrillo is also a senior associate chief and a top Aguilar aide.

Customs and Border Patrol spokeswoman Kristi M. Clemens told The Washington Post the agency "takes all allegations of misconduct or abuse extremely seriously" and that Commissioner Robert C. Bonner, who heads CBP, "has the highest confidence in Chief Aguilar's leadership and management abilities."

All the kickback allegations of travel improprieties "were investigated and adjudicated," she told the Post. "Those responsible were held accountable."