Toh was treating Teh for his heart condition and has every right to sign the death cert if he wanted to but rightfully chose not to.
As the daughter in law Pathologists attached to the Forensic Medicine Division cannot sign off when bodies are conveyed to mortuary unless they did the autopsy. No autopsy was done. The duty Coroner or the Inspector of Death however can. Both of them of them did not. That leaves a medical doctor and that mystery remains.