Sen. Joseph Lieberman, I-Conn., chairman of the Homeland Security and Governmental Affairs Committee, speaks Sunday on CBS's "Face the Nation" in Washington. (Mary F. Calvert/AP)

A 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 and Governmental Affairs Committee Chairman Joseph I. 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 E. 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 on April 11 by members of the security team sent to prepare for Obama’s arrival at a regional summit 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 on April 9, two days before the events surrounding the prostitution scandal, according to the Associated Press.

“Now 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 said during an appearance on CBS’s “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.”

At least four congressional committees are receiving daily briefings from Secret Service officials as the investigation continues, and the House Oversight and Government Reform Committee and the House Homeland Security Committee have made formal requests for full information on the scandal by as early as Friday.

Lawmakers from both parties on Sunday continued to voice support for Secret Service Director Mark Sullivan and his investigation while expressing amazement at the risky behavior of agents in Cartagena.

Several lawmakers said they expect more Secret Service employees involved in the scandal to be removed soon.

“I think we have some bad actors here, but I don’t think that we judge the Secret Service by its weakest link,” Rep. Elijah Cummings (D-Md.) told CNN’s “State of the Union,” adding later that “you can’t legislate people not being stupid, but certainly you can uphold the high standards of this organization.”

House Homeland Security Committee Chairman Peter King (R-N.Y.) said on NBC’s “Meet the Press” that he had “full confidence” in Sullivan.

“From every indication I’ve seen, from the moment this scandal broke until now, there’s no attempt to cover anything over,” he said. “Every possible lead is being examined.”

Sen. Susan Collins (R-Maine) also suggested the scandal could have been avoided if the Secret Service, which is nearly 90 percent male, employed more women.

“I can’t help but wonder if there’d been more women as part of that detail if this ever would’ve happened,” she said on ABC’s “This Week.”

Staff writer Dan Eggen contributed to this report.