It was billed as the largest exhibition of famous diamonds ever and featured such blockbuster rocks as the 203 ct. D Flawless De Beers Millennium Star and the 407.48 ct. Incomparable.

But after police warned that criminals could be planning a violent robbery, the Natural History Museum in London decided to close the exhibit—three months early.

“The museum’s priority is the safety and security of our visitors and staff,” museum director Michael Dixon said in a statement. “Based on police advice, the only responsible course of action in this situation was to close the exhibition with immediate effect.”

According to local press reports, police had noticed several “suspicious” visitors who took more interest in the security surrounding the gems than the actual stones. Some worried about a hostage situation.

The exhibit attracted 70,000 people since it opened in July.

The Millennium Star was the target of a foiled robbery in London in 2000.