Steve Thoburn did die at age 39, and contemporary reporting described it as a suspected heart attack after chest pains. But the causal part of the claim — that he died "because of the hassle" from the metric prosecution/publicity — is not established by the public evidence. A later Independent article on the case says that whether the stress of the conviction and being in the public eye contributed to his death is something "we will never know," which is consistent with uncertainty rather than proof of causation. So the death is verified, but the claimed cause→effect link is not. Sources: Legacy.com / San Diego Union-Tribune obituary; The Independent article on Steve Thoburn and the metric martyrs.