With meticulous planning and remarkable good fortune, the thieves who broke into a safe deposit in London's diamond district seemed to have pulled off the perfect jewel heist. But their luck ran out Tuesday when more than 200 Scotland Yard officers closed in on them.

The nine arrests were a triumph for embattled detectives whose early work had been criticized because of an embarrassing failure to respond to a midnight alarm at the start of a holiday weekend. That gave the thieves more than 48 hours to carefully remove the contents of the safe used by jewelers in the Hatton Garden district.

The suspects, all British men between ages 43 and 76, were questioned in a London police station after coordinated morning raids in northern London and the southeastern district of Kent, Scotland Yard said.

It said bags containing a significant amount of high-value property were recovered at one of the addresses but did not assign a value to the heist.

The audacious robbery over the Easter weekend fascinated Britain. Dressed in fluorescent vests and hard hats, the thieves entered the high-security vault area in the London diamond district, carrying bags and wheeled garbage bins for carrying off the booty.

To gain entry, they climbed down an elevator shaft and drilled through concrete walls that were 2 meters (6 feet) thick, later making off with the contents of 72 safety deposit boxes.

Commander Peter Spindler on Tuesday defended the police performance in the face of the earlier criticism.

"At times we've been portrayed as if we have acted like Keystone Cops but I want to reassure you that in the finest traditions of Scotland Yard, these detectives have done their utmost to bring justice to the victims of this callous crime," he said.

Nonetheless, police took the unusual step of apologizing for mishandling the alarm.

"Our call-handling system and procedures for working with the alarm-monitoring companies were not followed," they said. "Our normal procedures would have resulted in police attending the scene, and we apologize that this did not happen."

They asked victims to be patient while police sort out the recovered valuables in order to return them to their owners. They said the investigation is still expanding and appealed to the public for information.

Apparently no one took notice of the group as it went about its business in the diamond district that was nearly deserted over the holiday weekend.

Security footage showed the men, wearing dust masks, entering and leaving the building repeatedly after their arrival late on Thursday, April 2. They worked throughout the night and left Friday morning, returning on Saturday night and leaving again on Easter Sunday morning.

They had picked their spots carefully -- local jewelers routinely store valuable gems in the Hatton Garden Safe Deposit facility overnight and on weekends.

The facility's intruder alarm sounded shortly after midnight on April 3, but police did not respond -- although they asserted Tuesday that a private security guard did check the outside of the premises and found nothing amiss.

The crime was not discovered until the jewelry district sprang back to life Tuesday morning.