File FIR agasint the company, preferably agasint the head of company and officer in charge. Police will remand medical report from them. Only hospital report.
IN FIR also mention that he may have killed to usurp his PF, Gratuity or any other benefits like any term insurance done from their end to compensate or not providing medical report just to avoid last benefits payable to brother heirs.
Submit complain agasint the company to ministry of external affairs also to summon medical report to ascertain exact cause of death. Your case comes under fatal accident act if organization delayed to the treatment. Medical negligence impose on doctor/hospital.
You cannot claim medical negligence against the hospital from India, Case will file in Nigeria only.