An internal garda investigation has been launched into how a suspected quantity of drugs went missing after a drug seizure in Athlone, and then reappeared six years later.

RTÉ's This Week has learned that the investigation is looking at how the drug seizure was not formally recorded or stored at the time of the original raid on a premises in 2012.

The re-emergence of the drugs has also led to questions about whether a prosecution should have taken place at the time arising from the seizure, or whether the non-recording of the drugs impacted any other case that was prosecuted or not.

The issue has emerged at the same time as other matters relating to drugs policing in Athlone are also being examined internally in the force, and by the Garda Síochána Ombudsman Commission (GSOC).

One garda whistleblower has alleged that a long-serving member of the force had been colluding with a major drugs criminal in Athlone, and assisting the drugs gang to sell mostly heroin in Westmeath, Laois, Longford and Offaly.

Garda Nicky Keogh's allegations have been raised in the Dáil, and he has also alleged that he was subject to mistreatment within the force after he made his concerns about the alleged collusion known.

RTÉ understands that one of the gardaí, who was involved in the initial raid that led to the seizure which went missing for several years, is also closely connected to the collusion allegations made by Garda Keogh.

Among the issues which are being examined by the internal Garda investigation are; why the material taken in the drugs seizure was never properly admitted in any record; not stored appropriately, and therefore never adequately analysed.

The Garda Press Office said it was not in a position to comment, "to avoid prejudicing any further action that may or may not arise".