In Ruan v. United States, the Supreme Court held that a defendant who was convicted of conspiring to commit an offense against the United States must have knowledge of all elements of the conspiracy in order for his conviction to stand. The case arose when Mr. Ruan was charged with conspiring to defraud and steal from the government by submitting false claims for reimbursement under Medicare Part D, a federal health insurance program administered by private companies on behalf of Medicare beneficiaries. In affirming Mr. Ruan's conviction, however, the court found that he had not been adequately informed about one element—that is, that he knew or should have known that his actions would result in fraud or theft against the government—and thus reversed and remanded his sentence back to lower courts for further proceedings consistent with its opinion.

In the case of Ruan v. United States, the Supreme Court was asked to decide whether the government could be held liable for the death of a Chinese immigrant who was killed while attempting to enter the United States illegally. The majority opinion held that the government could not be held liable for the death, as the immigrant had voluntarily assumed the risk of entering the country illegally. Justice Stevens, however, wrote a dissenting opinion in which he argued that the government should be held liable for the death of the immigrant. He argued that the government had a duty to protect the immigrant from harm, and that the government had failed to do so. He further argued that the government had a duty to ensure that the immigrant was not subjected to any unnecessary risks, and that the government had failed to do so. He concluded that the government should be held liable for the death of the immigrant, as it had failed to fulfill its duty to protect him.