A federal grand jury on Wednesday indicted a San Francisco-area couple on charges of conspiring to steal trade secrets from DuPont & Co (DD.NYSE) and sell them to Chinese companies for more than US$20 million in contracts, The Wall Street Journal reported. The indictment, which came after a year-long investigation which saw Walter Liew, a US citizen, detained for seven months, charged that Liew and his wife Christina Liew had hired former DuPont employees to gain information on the company's practices for manufacturing titanium dioxide, a compound used in paints with military and aerospace uses. Prosecutors have filed letters and emails in which Liew allegedly wrote that a Chinese government official told him to develop expertise in titanium manufacturing and that he might sell the technology to Chinese companies. Prosecutors also charged that Liew and his associate advised state-owned company Pangang Group between 2003 and 2008 on constructing a titanium-manufacturing plan. Liew's lawyers have said the documents are not accurate.