The revolutionaries said Arsen Voskanyan, a Russian subject of Armenian source, was shot dead in April.
He was stole in November, the dissidents stated, blaming him for gathering noxious frogs to carry abroad.
The revolutionaries are holding peace converses with the Colombian government, however say they are probably not going to deny their seizing arrangement soon.
The ELN, or National Liberation Army, funds its operations for the most part with the payoff paid to discharge prisoners.
The declaration of Mr Voskanyan’s passing comes toward the finish of the third round of peace transactions, which started in February.
The dissidents said Mr Voskanyan was being taken to a remote wilderness range in north-western Colombia where he would have been given over to Red Cross delegates and liberated.
He all of a sudden snatched a projectile from one of the contenders and attempted to flee when he was shot dead, the ELN said. The data has not been affirmed by the Colombian government.
The ELN and the Colombian government are wanting to imitate the achievement of peace transactions with the bigger left-wing Farc revolt gathering.
Following four years of talks the Farc consented to a peace arrangement last November.