Russian authorities had put Antonio Valdes Garcia, who was on bail during his trial, under police guard, but he managed to slip away.
Valdes Garcia, a dual Russian-Spanish citizen, was a former general manager of a Yukos-affiliated trading company. He was charged as an accomplice, with jailed Yukos founder Mikhail Khodorkovsky and others, in the alleged embezzlement of $13 billion.
Chaika denied Valdes Garcia was a key witness in Yukos-related court cases.
The prosecutor-general also said today that new money-laundering charges will be filed against former executives of the bankrupt oil company, including Khodorkovsky.
Khodorkovsky is serving an eight-year prison term for fraud and tax evasion. His conviction and the state-run attack on Yukos were widely seen as politically motivated.