"Basically, they were documenting things that had never happened," Costello said.
"Who does that?" he asked. "Not somebody who makes an honest mistake, for sure. There were no honest mistakes here."
Brown has been charged with defrauding four charter schools that she founded of $6.7 million and then participating in a scheme with two other former administrators to cover it up.
"There was only one person who benefited, and she benefited financially, and that was June Brown," Costello said.
He stressed that the money Brown had collected from the fraud came from taxpayers and was intended to educate Philadelphia children at the three elementary charter schools she established and students from across the state who were enrolled in the Agora Cyber Charter School.
Costello said that the government's evidence showed that, in two years alone, Brown collected $4.27 million from the schools: $1.6 million in 2007-08 and $2.67 million the next year.
Brown may have started out as an educator, but her actions showed she was motivated by money, Costello said.
"The big lie in this case," Costello said, was that Brown's schools were run by independent boards, as is required by state law. In fact, he said, board members were Brown's employees, former employees, relatives, and their friends.
Costello said several former employees, including former business manager Anthony Smoot, who has pleaded guilty, have described creating backdated documents and forging signatures at Brown's request.
"He was just like everybody else who worked for Dr. Brown," Costello said. "He did what he was told and never questioned it."
Standing in front of the jury box, Costello said the government was asking the jurors to apply their common sense, think about the massive evidence, and do what no one who had worked for Brown or served on the boards of her schools had ever done: "Hold her accountable."
He urged the jury to find Brown and codefendants Michael A. Slade Jr. and Courteney L. Knight guilty as charged. Slade, Brown's great-nephew is a suspended chief executive of one of her charters. Knight, a teacher, is the former CEO at another.
Lawyers representing the three defendants will give their closing remarks when the trial resumes Wednesday.