A staff aide to Rep. Sam Farr, D-Calif., will testify on Thursday in a probe that could determine whether to file charges against Democratic Rep. Cynthia McKinney for allegedly striking a Capitol Police officer, FOX News has confirmed.

Farr's office confirmed that the staff aide was subpoenaed as a witness in front of a grand jury. FOX News also confirmed that a second congressional staff aide has been called to testify, but for reasons of confidentiality, the identity of the aide was being kept anonymous.

The aides' appearances mark the first indication that the U.S. Attorney's office is convening a grand jury to determine if an incident last week involving the congresswoman merits prosecution. The U.S. Attorney's office could not discuss any grand jury subpoena, but told FOX News the investigation continues. Spokesperson Channing Philipps said that no warrant has been issued in the matter.

McKinney, the six-term Georgia Democratic congresswoman, was bypassing a metal detector while entering Longworth House Office Building when asked by the officer to stop and go through the checkpoint. She allegedly turn around and beat the officer's chest more than once.

Outgoing U.S. Capitol Police Chief Terrence Gainer said he thinks prosecutors should bring a case against McKinney. Gainer told FOX News on Wednesday that he doesn't think the police officer's decision to stop the congresswoman was an incident of racial profiling as McKinney claims.

"I'm troubled by all the economics going into this, and the U.S. Attorney's office here has a lot of other crimes to look at ... But on the other hand, the member's not acknowledging at all that what she did was incorrect and now she's putting up the smoke and mirrors that we're racist and it was done because she's black, that's wrong," Gainer said.

The officer "didn't see the woman wear the badge that she should have had on, and called out to her, didn't recognize her facially, called out to her, she breezed passed, called out again and reached out and grabbed her hand, her arm. When she came around she hit the officer in the chest," Gainer alleged. All congressional members are given a lapel pin that identifies them as an elected representative. That identification permits them to skip the security checks.

McKinney has not admitted to hitting the officer, and she has rejected claims that the police officer didn't recognize her because she altered her appearance. McKinney recently changed her trademark hairstyle from two tight french braids to looser curls that surround her face.

"What I would say, however, is that (this is) much ado about a hairdo," McKinney told FOX News, saying that the officer should be able to recognize every congressional member.

Officers are required to screen approximately 30,000 people entering the building each day.

Just Monday, Capitol Police had to evacuate the Capitol Building as a result of a power failure that triggered emergency procedures. McKinney, however, said the incident involving her is part of a larger problem of the Capitol Police mistreating blacks.

"We have 39 young people visiting from the state of Georgia, all of whom were African-American. And they had a very, very negative experience with the Capitol Hill Police. Two hundred-fifty black police officers have filed a lawsuit against the Capitol Police," she said.

"What I have suggested and what many other people have, quite frankly, suggested is that the issue of racial profiling needs to be one that is discussed and dealt with by the American people," she said.

Gainer rejected the idea that the incident is one of racial profiling. He said the police had all they need to arrest McKinney last Wednesday at the time of the incident, but police passed the information to the U.S. attorney's office so they could look at the evidence and build a case.

"There would be no reason to go to the U.S. Attorney's office if we didn't want to have an arrest," Gainer said.

Meanwhile, the top House Republican, Speaker Dennis Hastert, said Wednesday that members of Congress should respect the job of the police to protect the Capitol complex.

"This is not about somebody's ego. It's not about racial profiling. It's about making this place safer and working with the people that try to make it safer," said Hastert, R-Ill.

Several Republican members were wearing pins on Wednesday that said "I Love Capitol Police" as part of a campaign to support a House resolution expressing appreciation for the job the Capitol Police do each day. The resolution commends the police for their professionalism toward members of Congress and visitors, even though they "endure physical and verbal assaults in some extreme cases."

"I don't think it's fair to attack the Capitol Police and I think it's time that we show our support for them," said Rep. Patrick McHenry, R-N.C., a sponsor of the measure. Ignoring a police officer's order to stop, or hitting one, "is never OK," McHenry said.

Some GOP members have said the McKinney incident serves to underscore Democratic insensitivity to security concerns. Democrats have countered that Republicans are more interested in making an issue of this than looking at their own problems, for instance, the underlying lobbying and campaign finance-related troubles that contributed to Rep. Tom DeLay's announcing his resignation on Tuesday.

Still, McKinney has won little support among her fellow Democrats in the feud. In a press conference last week she was joined by no House members, and instead featured prominent black activists, actor Danny Glover and singer Harry Belafonte.

House Minority Leader Nancy Pelosi, D-Calif., said Tuesday she can't think of a set of circumstances that would justify striking an officer. McKinney denied that she and Pelosi are not on speaking terms, and avoided naming elected officials who have offered her support.

"The most important support that I have is from the people of the 4th Congressional District," McKinney said of the Atlanta district she represents.

FOX News' Molly Henneberg and The Associated Press contributed to this report.