Arlington police said Officer Thomas Kantzos, a 17-year-old veteran of the department, was arrested by the FBI Tuesday as part of a continuing joint investigation with federal and state authorities.
Officer David Vo, another officer who was facing charges in the same investigation, committed suicide on Tuesday, police said.
Vo, 34, had been arrested last weekend and released pending charges.
A third employee of the police department, Officer Craig Hermans, 34, was placed on administrative leave after being questioned in connection with the criminal probe.
"Criminal misconduct by our employees is intolerable as it damages the trust and confidence of those we serve," said Arlington Police Chief Will D. Johnson in a written statement. "We will always aggressively pursue the arrest and prosecution of any employee engaged in this sort of behavior."