Prosecutors investigating a suspected case of large-scale stock manipulation conducted through the investment consulting firm, SG Securities Korea, detained a key figure in the scandal on Tuesday.

The Seoul Southern District Prosecutors' Office, together with financial authorities, apprehended Ra Deok-yeon, the head of a consulting firm, at his residence.

Ra is suspected of trading concerned stocks at a predetermined price and time after taking over investors' mobile phones and securities accounts, thereby inflating trading volumes and prices.

The investigation will also focus on Ra's alleged laundering of criminal proceeds through an unrelated corporate entity, and evading taxes.

Prosecutors formed a joint team with financial authorities to investigate the suspicious trading after shares of eight local companies that had been steadily rising since April of last year suddenly began to plummet.

The stock plunge followed mass sell-offs through SG Securities Korea, the local branch of the Societe Generale Group of France.