WASHINGTON — The former top watchdog for the Department of Homeland Security rewrote reports and slowed investigations at the request of senior staff for then-Secretary of Homeland Security Janet Napolitano, a review conducted by Senate staff found.

Charles K. Edwards, who was the acting inspector general for DHS from late 2011 through early 2013, considered aides to Napolitano to be friends, socialized with them over drinks and dinner and, at their urging, improperly made changes to several investigative reports, according to the Senate review released Thursday.

Napolitano left DHS in September to become president of the University of California system.

Edwards “failed to uphold the independence of the DHS Office of Inspector General” and “directed reports to be altered or delayed to accommodate senior DHS officials,” the scathing 27-page report says.

At the request of DHS officials, the report alleges, Edwards changed the wording and the release date of an audit of Secure Communities, a controversial program that alerts immigration agents when someone who is illegally in the country is booked into a local jail. The audit, conducted at the request of lawmakers, looked at whether immigration officials had made misstatements to local officials during the implementation of the program.

In one email reviewed by Senate staff, Edwards asked Napolitano’s legal adviser, John Sandweg, which day would be good to release the Secure Communities audit. Edwards then “directed the audit to be released on the date provided,” the report says.

The review did not substantiate allegations that Edwards had changed or withheld information for reports on the misconduct of Secret Service agents who hired prostitutes in Cartagena, Colombia, during a visit before a 2012 presidential trip.

The 10-month investigation was led by Sens. Claire McCaskill, D-Mo., and Ron Johnson, R-Wis., the top-ranking members of the Homeland Security subcommittee on financial and contracting oversight.

Johnson said he was troubled by the conclusion that Napolitano’s senior staff was seeking to influence the inspector general’s work.

Edwards spent nearly two years as the acting inspector general. Ten employees who worked for Edwards told Senate staff that his pursuit of a permanent appointment to the post appeared to threaten the independence of the office. Edwards told investigators the allegations were untrue.

Johnson said the Obama administration should never have allowed Edwards to hold the temporary post for so long. Congress should prohibit acting inspector generals from being considered for the permanent job, he said.

Napolitano would not comment on the report because she was not named by Senate investigators as one of the DHS officials who was in contact with Edwards, said Steve Montiel, a University of California spokesman for Napolitano.

Edwards resigned from the inspector general’s post in December, three days before he was scheduled to appear in front of the Senate subcommittee that investigated him. At his request, DHS officials transferred him to a job in the office of science and technology. He has worked for the federal government for two decades and has experience in computer engineering.

On Thursday, the new secretary of Homeland Security, Jeh Johnson, said he had placed Edwards on administrative leave. “Other individuals who are apparently and allegedly implicated have already left DHS and if additional information comes to light, I will continue to take appropriate action,” he said.

Senate investigators also concluded that Edwards had enlisted help from an employee to write his doctoral dissertation and had retaliated against employees who reported his alleged misconduct. Investigators did not find evidence to confirm allegations that Edwards had violated anti-nepotism laws.