In 2008, Gertz was subpoenaed to the Santa Ana, California federal court to testify in the case of Chi Mak, who was convicted of providing United States Navy technology to China. Gertz refused to answer questions about his sources, citing the Fifth Amendment.

During 1996 Gertz reported in the Washington Times on Chinese sales of nuclear technology to Pakistan. In 1997 he reported on Russian aid to Iran's nuclear weapon program, based on information given him by the Israeli intelligence agency Mossad. In 1998 he reported on United States sale of missile technology to China. In 2004, Gertz claimed that Syria, possibly with the aid of Russian troops, transferred Iraqi weapons of mass destruction stockpiles to its own military installations.