Actually there is no “burden of proof” needed to pursue legitimate lines of. investigation. When a DNC staffer is murdered, any legitimate investigation should consider possible motives relating to his work at the DNC. You don’t have to be Sherlock Holmes: even an average detective would look there. You don’t need to prove anything or cite evidence: the purpose of the investigation is to turn up such evidence if it exists. The need for a high level investigation by the FBI or similar agency is to ensure there are adequate resources and to satisfy the public as to the integrity of the investigation. The more that people argue against a full investigation of the Seth Rich murder, for example, by inventing new and previously non-existent burdens of proof to pursue an investigation in any plausible direction, the more it becomes clear we need to have a thorough examination — one that can hopefully solve his murder. What are you afraid will be found?