SAN FRANCISCO – Federal authorities said Wednesday that an employee of “expert network” firm Primary Global Research LLC has been arrested on insider-trading charges.

The arrest marks a major development in a massive government investigation into possible insider trading by hedge funds and mutual funds, and it represents the first arrest at the types of research firms that are the focus of the widening probe.

The investigation is continuing, noted Preet Bharara, U.S. attorney for the Southern District of New York.

Authorities said Don Ching Trang Chu, known as Don Chu, was arrested Wednesday morning on conspiracy charges in connection with his employment at an “expert-networking” firm.

Such firms connect consultants with investors looking for detailed information about industries and companies.