At the time, Grewal acknowledged it could have been a clerical error at the courthouse and asked Estrich to confirm whether she had been admitted to practice before the court.

On Thursday, she filed papers requesting admittance and moments later that began with a belief that she had been admitted to the Northern District court.

"The basis of my belief was that when I moved to California in 1986 I joined a law firm and believed that the law firm facilitated and assisted me in complying with the administrative requirements for my admission to the District Courts in the state. In addition to the Central District of California, I am admitted to practice before the United States Court of Appeals for the Ninth Circuit, and the United States Supreme Court," the explanation read.

"That law firm has since dissolved. As a result of these circumstances, I did not confirm my membership to practice before this Court. My omission was through inadvertence and oversight, and my conduct was not willful," said the explanation.

In his notice on Wednesday, Grewal held out the possibility of penalties but didn't specify what they might be.