Police are investigating how three domestic helpers with a joint income of $10,000 could have become $300,000 loansharks. Triad investigators were questioning the source of start-up funds after the three domestic workers were arrested in Shamshuipo and Tin Shui Wai last week. The trio - two sisters and a male partner - are believed to have operated their mobile money-lending agency from Chater Garden in Central for three years. Detective Senior Inspector Tommy Tang Wai-keung said yesterday their combined monthly income was $10,000, yet they managed to run the $300,000 agency from the district where many of Hong Kong's 127,000 maids gathered on Sundays. At least 20 of the alleged 50 victims said they had been forced to pay interest of up to 133 per cent on loans of $100 to $60,000. The three, aged 33 to 41, offered loans to maids who needed emergency money to send home. Victims were forced to sign IOU agreements for high interest rates, submit photocopies of their passports and provide addresses and phone numbers. 'The only difference between local loansharks and the Filipinos is that Filipinos use less force and violence. They issue their threats in phone calls,' Inspector Tang said. Police began investigating after a maid complained when her phone threats began escalating last month. The trio would be charged with operating without a licence and charging excessive interest, police said.