Seth Rich’s death involved suspicions that he was the source of the DNC email leaks.
No other theories are supported by the facts.
It is very rare that an on-street late night murder is for anything else than a nervous robber needing money or things he can steal and sell and a target resisting giving it up. In this case, there is no evidence that anything of value was taken, as Mr. Rich’s cell phone, watch and money were on his person when discovered. There is also no sign of a struggle. Why would a street criminal shoot someone, risk being caught, and take nothing from the fruits of their crime? This has always looked like a hit, instead. What would be the source of that?? Relationship discord, heavy gambling debts, jealous coworkers? No evidence of any of that. Per Sherlock Holmes, “When you have eliminated the impossible, no matter how improbable that which remains, must be the truth”. I suspect that the improbable in this murder case was that Mr. Rich was hit because he either knew too much or someone wanted to stop him on acting on what he already knew.