The Justice Department is examining whether scandal-plagued German payment company Wirecard AG played a critical role in an alleged $100m bank-fraud conspiracy connected to an online marijuana marketplace, according to people familiar with the investigation.

Two businessmen have already been charged in the alleged fraud, accused of conspiring with third-party payment processors and others to trick US banks into approving credit-card payments for marijuana products. The men were able to do this, prosecutors said, by using phoney companies with accounts at offshore merchant banks that in turn earned steep fees off the transactions.