South Korean prosecutors said Saturday they have arrested the son of the country's largest pyramid schemer and the conman's mistress for their alleged involvement in concealing huge profits from the investment fraud.

Cho Hee-pal, who has been at large since 2008, is suspected of swindling about 4 trillion won (US$3.5 billion) from an estimated 50,000 people between 2004 and 2008, according to prosecutors. Cho is rumored to have died from cardiac arrest in China four years ago, but his death has not been verified.

Prosecutors said they requested on Friday that a local court issue a warrant to detain Cho's 30-year-old son, whose identity is withheld, on suspicion of concealing part of the money that his father had swindled.

Earlier in the day, they also arrested a 55-year-old woman, only identified by her surname Kim and who is known as Cho's mistress, for allegedly concealing profits worth 1 billion won in connection to Cho's crime.

In September last year, prosecutors re-opened their probe into the allegations against Cho. (Yonhap)