A federal grand jury arrived Thursday at the U.S. District Court in Washington, D.C., to hear from two House staff aides about a scuffle last Wednesday involving a Capitol Police officer and Democratic Rep. Cynthia McKinney.

Meanwhile, McKinney, made a formal apology on the House floor for the incident, saying "there should not have been any physical contact."

"I am sorry that this misunderstanding happened at all, and I regret this escalation, and I apologize," she said to applause. McKinney also said she would support a House resolution introduced by Republicans to express appreciation for the work done by Capitol Police.

Set to testify Thursday were Troy Phillips, legislative assistant to Rep. Sam Farr, D-Calif., and Lisa Subrize, executive assistant to Thaddeus McCotter, R-Mich. Phillips reportedly saw the incident in which McKinney allegedly beat a Capitol Police officer's chest after he supposedly put his hand on her arm to stop her forward progress after she bypassed the Longworth House Office Building metal detector.

Lawmakers are permitted to skip the security checkpoints if they are wearing a congressional lapel pin that identifies them as an elected official or if they are recognized by the police. The six-term Georgia Democratic congresswoman was not wearing her pin.

The U.S. Attorney's office could not discuss any grand jury subpoena but told FOX News the investigation is continuing. Spokesperson Channing Philipps said that no warrant has been issued in the matter.

Former U.S. Capitol Police Chief Terrence Gainer, whose last day on the job was Wednesday, said he thinks prosecutors should bring a case against McKinney. Gainer told FOX News 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 Wednesday.

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.

Prior to the apology, McKinney had not admitted she struck the officer, and she has rejected claims that he 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 on Wednesday. She also has claimed that her being stopped is due to racial profiling. The police officer who stopped her is white.

She said since she is one of only 14 black female representatives, she shouldn't be that hard to recognize by Capitol Police. But others say McKinney has a history of racially charged accusations.

Former House Majority Leader Tom DeLay, who on Tuesday abandoned his re-election bid after becoming the poster boy for Democratic campaigns against corruption in Congress, called McKinney a racist.

"She has a long history of racism," DeLay, R-Texas, told FOX News. "Everything is racism with her. This is incredible arrogance that sometimes hits these members of Congress, but especially Cynthia McKinney."

DeLay also sent an open letter to the Capitol Police, thanking them for the service they do. Almost eight years ago, Capitol Police Officer John Gibson was shot and killed by an assailant in DeLay's office. The man, a former mental patient who also started chasing a tourist through the building, pulled out a gun while passing through the metal detectors. He also shot and killed another officer, Jacob J. Chestnut, outside Delay's Capitol offices.

Gainer rejected the idea that the incident is one of racial profiling. House Speaker Dennis Hastert said Wednesday the issue is about respect for the work the Capitol Police do.

"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.