WASHINGTON – An independent U.S. senator who caucuses with Democrats joined a Republican colleague Sunday in calling for an expanded probe of the Secret Service prostitution scandal, saying the investigation should also include a look at White House personnel assigned to prepare for President Obama’s trip to Colombia.

There is no evidence that White House employees knew about the misbehavior. But Senate Homeland Security Committee Chairman Joe Lieberman, I-Conn., urged the Obama administration to conduct an investigation “just to make sure that none of them were involved,” echoing demands from Sen. Charles Grassley, R-Iowa.

“The White House advance person knows exactly where the president is going to be at any time,” Lieberman said on “Fox News Sunday.” “If anybody thinking the worst wanted to attack the president of the United States, one of the ways he might find out the path that he would follow in Cartagena is by compromising White House advance personnel.”

The remarks come amid a continuing uproar over a night of heavy drinking, visits to strip clubs and payments to prostitutes about 10 days ago by members of the security team sent to prepare for Obama’s arrival at a regional summit meeting in Cartagena, Colombia.

The scandal has implicated 12 Secret Service employees and 11 members of the military. Six of the Secret Service employees have lost their jobs, five are on leave and one has been cleared of “serious misconduct” but will face administration action, officials have said.

A new wrinkle in the case emerged Sunday amid reports that one of the Secret Service employees was staying at a Hilton later occupied by Obama. The employee is under investigation for alleged improprieties that occurred several days before the events surrounding the prostitution scandal, according to The Associated Press.

“We don’t know at this point what that 12th agent is being charged with and why he’s been put on administrative leave,” Lieberman told CBS’ “Face the Nation.” “But now you’re into the hotel where the president of the United States was going to stay. And it just gets more troubling.”