after a quadbike was found overturned on the A465 westbound between Rhymney, Caerphilly, and Dowlais, Merthyr Tydfil, at around 04:50 BST on Saturday.
A 40-year-old man from Merthyr Tydfil has been arrested on suspicion of murder and driving while unfit through drink and driving while unfit through drugs.
A second man, a 37-year-old from Merthyr Tydfil, has been arrested on suspicion of perverting the course of justice and assisting an offender.
Both remain in police custody.
Police believe a second vehicle – a white BMW found burned out in the Dowlais area – may have been involved in the crash.
