A swastika was daubed in a police station in north London in an area only police officers and staff can access.
The graffiti was discovered by police in Edmonton Police Station in February and deemed a "faith-based hate crime" - but a lack of forensic leads meant the case was closed without identifying a suspect.
In a statement, a Metropolitan Police spokesperson said: "On 15 February 2019 graffiti was found on the wall in the lift lobby area of Edmonton Police Station. The graffiti, in biro, was a swastika symbol.
"The incident was recorded as a faith hate crime and a senior investigating officer at Detective Chief Inspector level was appointed to investigate the offence.
"The area the graffiti was found in was within the police station so not accessible to the general public. A thorough investigation was undertaken but no forensic opportunities were identified.
"As a result, it was not possible to identify who had drawn the graffiti. We take all hate crime seriously and have a zero tolerance approach."
Victor Olisa, a former senior officer and head of diversity at the Met, said "there could be someone with far-right sympathies who is confident to express that in a secure part of a police station", telling the Guardian: “People have been saying things are getting worse on diversity and equality in the Met."
He added the incident was "more extreme right wing" than faith-based crime.
Iman Atta, the director of hate crime documenting service Tell Mama, told the Guardian: “To have a swastika, a Nazi symbol, in an area which police officers and staff alone have access to, is worrying.
“While this is an isolated incident, it is deeply concerning. This also raises questions about the institution and whether such incidents are truly isolated.
“The local force should undertake a thorough investigation to reassure communities that there is zero tolerance towards any form of racism within the force.”
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