The investigation into the explosion at the Pembroke oil refinery which killed four workers reaches its third anniversary today, June 2.

A dedicated team of Dyfed Powys Police detectives and Health and Safety Executive (HSE) inspectors continue a joint criminal investigation into the explosion, which killed Robert Broome, Andrew Jenkins, Julie Jones and Denny Riley on June 2, 2011.

Another worker also suffered serious injuries.

A Coroner’s inquest into the deaths was opened shortly after the explosion by HM Coroner for Pembrokeshire and Carmarthenshire, Mark Layton, but was adjourned pending the outcome of the Police and HSE investigation.

The on-going investigation is seeking to establish whether a potential offence under the Corporate Manslaughter Act 2007 has been committed.

It is believed that this is one of the first times, since the introduction of the Act, that the use of this legislation has been considered against a large, multi-national company.

The complex nature of the inquiry has involved lengthy and detailed forensic investigations being undertaken by specialist staff from the Health & Safety Executive Laboratory and Specialist HSE Inspectors, with experience of the oil refining industry.

In addition to this, the investigation is supported by specialist lawyers from the Crown Prosecution Service’s Serious and Complex Case team and HSE.

Detective Chief Superintendent Simon Powell, the Senior Investigating Officer for this investigation said: “This is one of the most complex inquiries of this nature that Dyfed Powys Police has ever undertaken.

"However, the close partnership between the Police, Health and Safety Executive and other experts is ensuring that a very thorough investigation is being conducted which is gathering evidence to establish whether a prosecution should take place, and to provide the families with the facts surrounding the events that led to the deaths of their loved ones and the injuries that were sustained by the survivor.”

A team of Dyfed Powys Police Family Liaison Officers continue to provide support to the bereaved families.