Zatko, who served as Twitter security chief until he was fired earlier this year, received the subpoena on Saturday, the report said.
In July, Zatko filed a complaint with several US federal agencies, including the Securities and Exchange Commission (SEC), accusing Twitter of misleading federal regulators about security policies and spam.
Musk alleged earlier that Twitter undercounted its fake and spam accounts when he tried to purchase it for $44 billion, according to the report. Musk’s legal team is now demanding to hear from Zatko on the number of fake and spam accounts.
In April, Musk backed from a deal he signed on the acquisition of Twitter, saying he decided to abandon the decision to acquire the company because of concerns over the true number of spam accounts. Twitter sued Musk for abandoning the deal, but Musk countersued.