Allen was shot in front of his partner at his home in Buncrana.
An Garda Síochána are appealing to anyone with information in relation to the "heinous murder" of a 24-year-old man in his home 10 years ago.
Wednesday (9 February) marks the anniversary of the death of 24-year old Andrew Allen.
Allen was murdered by a group of individuals at his home in Links View Park Buncrana, Donegal on 9 February, 2012.
He was shot in front of his partner at approximately 9.20pm and was later pronounced dead at the scene.
A car believed to be involved in the murder was found on fire at Churchbrea, Fahan, three miles outside Buncrana shortly after the shooting.
Gardaí expressed gratitude for all witnesses that have come forward and made statements in the past, but they still believe there are people in both Buncrana and Derry who have information that could assist with the investigation.
In the course of the investigation, six people have been arrested and questioned, with 700 lines of enquiry followed.
Gardaí say they are continuing to investigate "this heinous murder" along with counterparts in the PSNI.
An Garda Síochána is appealing to anyone with information which may assist this ongoing investigation to make contact with them, as they say any assistance received could be instrumental in bringing the investigation to a successful conclusion.
Anyone with information can contact the incident room at Buncrana Garda Station 074 93 20540 or the Garda Confidential Line 1800 666 111.
