A criminal prosecution could still be brought over the death of a 16-year-old girl who fell 100ft from a theme park's roller coaster.
Hayley died following the accident in April 2004
Hayley Williams, from Pontypool, died in April 2004 when she fell from the Hydro ride at Oakwood, Pembrokeshire.
It was announced on Thursday no charges would follow the police investigation.
But the Health and Safety Executive (HSE) said a prosecution could follow its own ongoing inquiry. Oakwood said it was co-operating with the HSE.
Hayley died after falling 100ft from the Hydro ride on 15 April, 2004 during a day out at the park with her mother, sister and other friends during the Easter holidays.
Following a 21-month Dyfed-Powys Police investigation, the Crown Prosecution Service said on Thursday that no criminal charges would be brought over the case.
Hayley's parents, Alan and Beverley Williams, issued a statement in which they said they were "completely disillusioned and naturally angry" about the lack of charges.
But a spokesman for the HSE, which enforces health and safety regulation in the UK, later said its own investigation into the case could still result in a criminal prosecution.
Hayley fell 100ft from the Hydro ride at Oakwood Theme Park
The spokesman said: "The HSE investigation is continuing. As a result of this the HSE will look at the next steps they will take.
"This could result in no further action or enforcement action.
"Enforcement action could include criminal prosecution under health and safety legislation."
The HSE is unlikely to make any decision before the coroner's inquest, which Pembrokeshire coroner Michael Howells said could take place in the next six to eight weeks.
Responding to the HSE's statement, a spokesman for Oakwood Theme Park said on Saturday: "Oakwood is co-operating fully with the ongoing health and safety investigation."