Two Ukrainian nationals, including a woman, have been identified as the masterminds of the Ponzi scam that has duped hundreds in Mumbai after promising them big returns on their investment. The Economic Offences Wing of Mumbai Police, which is investigating the Torres jewellery scam, has zeroed in on the role of Ukrainian nationals Artem and Olena Stoin and is trying to track them down. According to police sources, the two played a key role in conspiring how people can be lured with huge returns on their investment in gemstones, gold and silver.