ATLANTA — The former chief operating officer of Atlanta’s High Museum of Art has pleaded not guilty to a federal theft charge in U.S. District Court.

Brady Lum is accused of using his position to embezzle more than $600,000 from the museum, according to federal prosecutors.

The U.S. Attorney’s Office in Atlanta says Lum doctored invoices and approved transactions to create a personal “slush fund.”

A statement from the Woodruff Arts Center previously said “financial irregularities” were first identified in December.

“While entrusted to run the High Museum, Lum allegedly used the museum’s money as his personal slush fund and thereby betrayed one of Atlanta’s civic crown jewels,” said U.S. Attorney Theodore S. Hertzberg. “Our office will move with swift precision to prosecute individuals who abuse positions of power and trust to enrich themselves at the expense of non-profit institutions.”

Prosecutors allege the funds were used to purchase luxury guitars, other music equipment, personal music lessons and woodworking tools.

Court documents say the alleged scheme involved falsified or inflated vendor payments routed through museum accounts over a period of time.

“We expect officials of one of our communities’ historic institutions to serve as stewards — not to loot it,” said FBI Atlanta Special Agent in Charge Marlo Graham. “The FBI remains unwavering in its pursuit to hold accountable those who exploit their positions for selfish purposes.”

Authorities have not said how the alleged activity was discovered, but say it triggered a federal investigation into the museum’s financial records.

Lum is scheduled to return to court for further proceedings.