Officers were today investigating claims a knife handed in during an amnesty was stolen from a police station and used in a murder.
Tony Wilkinson, 28, repeatedly stabbed Neil Hampson in the heart and neck during a party in Southampton, Hants.
Mr Hampson, 32, died in hospital after the attack in November 2007.
The murder weapon was never found but the jury at Winchester Crown Court was told that it could have been stolen from police after being handed in during an amnesty.
A friend of Wilkinson's worked as a police driver in charge of collecting handed-in blades from police stations across Dorset.
Wilkinson, from Poole, Dorset was found guilty of murder and jailed for life on Friday. He was told by the judge at Winchester Crown Court he would serve a minimum of 18 years.
A Dorset Police spokesman said today: "While the murder weapon has never been identified, during the course of the murder investigation a number of knives were seized by detectives.
"It was alleged during the trial that some of these knives may have been stolen from Dorset Police by a member of police staff after having been handed in during a knife amnesty.
"That member of staff had left the employment of Dorset Police a considerable time before the murder was committed and the knives recovered.
"An investigation into the circumstances surrounding the recovered knives is being undertaken by Dorset Police and whilst the investigation is ongoing it is not appropriate to discuss the matter further."Reuse content