Since then, however, Skief has used Harambee's debit card 40 times, racking up charges of $11,000 in cash and purchases, according to documents filed in U.S. District Court on Thursday.
"Following the entry of his guilty plea, the defendant walked out of the courthouse and resumed the fraud that resulted in the criminal charges to which he pleaded guilty," the government said in its filing.
Federal investigators said Skief used the card five times within nine days of his guilty plea.
Prosecutors have asked U.S. District Judge Paul S. Diamond to revoke Skief's $50,000 bail and detain him. He is scheduled to be sentenced Jan. 22.
Neither Skief nor his attorney, Scott A. Coffina, could be reached for comment.
First Assistant U.S. Attorney Louis D. Lappen said Skief's actions were unusual.
"Most people who sign a plea agreement do not go out of the courtroom and then return to the criminal activity they had pled guilty to," Lappen said Friday.
In the filing, prosecutors said that Skief had continued to be involved with Harambee's finances in violation of the terms of his plea agreement. He also failed to report to Pretrial Services on Sept. 9, as he had been directed to do.
When confronted, Skief said he woke up late that day and did not have time to report to Pretrial Services "because he was dealing with 'school business,' " court documents said.
Prosecutors said that Skief's actions demonstrate "an arrogance that is difficult to understand."
Skief, who had been a science teacher at the charter school earning $40,000, became CEO at Harambee and the related nonprofit in December 2007 after his father, John, died unexpectedly at age 59.
In the plea agreement, Skief admitted stealing more than $79,000 from Harambee Institute, which owns the charter school's building, and taking $9,000 from a scholarship fund created in the memory of his father. At the time of the plea agreement, sentencing guidelines suggested a prison sentence of at least 21 to 27 months.