London jewellery heist: police decided not to respond to intruder alarm alert
Police were alerted to an intruder alarm at the scene of the Hatton Garden safety deposit raid in London - but decided it did not require response.
Scotland Yard said an investigation has been launched into why a call from an alarm firm was given a grade that "meant that no police response was deemed to be required".
The Met Police's Central Communications Command received a call at 0021 on Good Friday stating that an alarm had gone off at Hatton Garden Safety Deposit Company.
Scotland Yard said in a statement: "The Metropolitan Police Service (MPS) has been making initial inquiries into what calls were received relating to the Hatton Garden burglary last weekend.
"At this stage we have established that on Friday, 3 April at 00:21hrs a call was received at the MPS Central Communications Command (MetCC) from Southern Monitoring Alarm Company.
"The call stated that a confirmed intruder alarm had been activated at the Hatton Garden Safe Deposit Ltd.
"The call was recorded and transferred to the police's CAD (computer aided despatch) system. A grade was applied to the call that meant that no police response was deemed to be required. We are now investigating why this grade was applied to the call. This investigation is being carried out locally.
"It is too early to say if the handling of the call would have had an impact on the outcome of the incident."
The disclosure comes after potential victims expressed anger at being left in the dark over the investigation.
Thieves disabled a communal lift shaft and climbed down to the basement before using power tools to break into the vault during the "sophisticated" raid in London's jewellery district.
Once inside, they opened up to 70 safety deposit boxes.
Calls to the central communications command are initially dealt with by a "first contact" operator, who grades all incidents "in terms of their urgency", according to the Met's website.
It says: "Upon receiving a call, information is recorded and passed on to the relevant department, or to a dispatcher for a police deployment if required.
"First contact operators will question the caller and gain all the relevant information necessary to ensure the best police response.
"Having completed this, the operator will grade the call in accordance with standard operating procedures for the type of incident. The grading will depend upon the urgency of the call."
Calls are passed to a despatch operator for deployment if required, the site says.
It adds: "Despatch operators receiving the incidents will assign the appropriate police resources depending upon the type of incident."