Manslaughter charges are being considered against bosses of the Chevron oil refinery where four people were killed last year.
Three men and one woman were killed in the massive explosion at the plant on 2 June in what was described as the UK’s worst refinery disaster for almost four decades.
Since then an inquiry is continuing into the cause of the explosion, which Chevron said happened while a storage tank was being taken out of service for maintenance work.
Those killed were Julie Jones, 54, a fire guard from Pembroke, and three men from Milford Haven: Dennis Riley, 52, Robert Broome, 48, and Andrew Jenkins, 33.
A fifth victim was left in a critical condition and is still understood to be undergoing medical treatment.
Following the blast, experts from the US flew in to assist its local investigators in the painstaking and lengthy process of investigation in to the tragedy.
Maintenance work had been carried out on a 730 m3 storage tank which exploded, damaging a container next to it.
Meanwhile, police have since continued to work with the Health and Safety Executive following a forensic examination of the scene.
Police have confirmed they are considering bringing manslaughter charges by gross negligence.
An employee of Velero Energy Limited, the company which now operates the refinery, has been interviewed under caution in relation to the investigation.
A police spokesman said: ‘Dyfed Powys Police can confirm that they have interviewed a male employee of velero Energyunder caution in connection with the explosion on June 2.
‘This man was interviewed in relation to potential offences of manslaughter by gross negligence.
‘This development is very much part of the continuing joint police and HSEinvestigation which is of an extremely complex nature, and no conclusions should be drawn at this stage.’
A spokesman for Valero said: ‘A this refers to an ongoing investigation by the HSE and the police, Valero Energy can offer no further comment on the explosion at the refinery, when it was owned and operated by Chevron.
‘Both Valero and Chevron continue to provide their full co-operation to the police and HSE investigation.’