Justin Bieber and Bon Jovi Concerts Scene of Stadium Heist

JOHANNESBURG, South Africa May 14, 2013— -- It's a scene seemingly ripped right from an "Ocean's Eleven" script.

Thieves targeted the city's famed FNB Stadium following concerts this weekend by Justin Bieber and Bon Jovi in a heist that included them chiseling through the wall of a safe room and lowering themselves into the room with ropes. And using a system of ropes and ladders to get back out.

Authorities are not disclosing exactly how much cash was stolen, but they believe most of the money had been collected from numerous bars, food stands and merchandise outlets.

No one even noticed the cash was gone until early Monday morning. Eyewitness News South Africa footage shows a crime scene littered with roof debris and busted bricks.

"It wasn't an impromptu incident," Jacques Grobbelarr, a member of the stadium's management team, told Eyewitness News South Africa. "There was definite planning. Looking at the scene and the place they broke into, it looks as if they were planning this for quite some time, probably a couple of days."

Private investigators have been brought in to help police, and several employees have been given polygraph tests, as authorities believe only those with an intimate knowledge of the stadium's layout and security plans could have pulled off a heist of this caliber. Officials are also combing through footage from 10 security cameras around the stadium, which remains on lockdown.

The stunning robbery came just hours after Bieber wrapped up a Sunday concert for more than 60,000 fans. After learning of the heist, Bieber denied any involvement, telling TMZ, "It' wasn't me."

Bon Jovi also performed at FNB stadium over the weekend for a large crowd, meaning the suspects picked a lucrative weekend to strike.