Surrey Police has confirmed it previously confiscated guns from the scene of a double murder investigation in Farnham.
In a statement, it said a shotgun licence and several licensed guns had been taken from the address in May last year, but were returned just a couple of months later.
The force has referred itself to the Independent Police Complaints Commission.
– Surrey Police statement
Surrey Police had had previous contact with parties involved in this incident and has referred a past contact to the IPCC.
In May 2013 a shotgun licence and a number of licensed shotguns were seized from the address however the licence and guns were returned in July 2013.
We are in the process of establishing if one of these licensed guns was the firearm recovered on Sunday.
Surrey Police is reviewing the return of the licence to ensure compliance with Home Office guidelines and has referred this matter to the IPCC."
The IPCC has confirmed it is considering the referral.