Expert witnesses are morally and legally obligated not to lie, and hence not to withhold information requested under cross-examination from opposing attorneys. Yet expert witnesses are not legally required in all situations to volunteer information and opinions that damage the case of the attorney who hired them. For example, an engineer might know of a test that could shed further light in a liability case, but which was not conducted because of its prohibitive cost. The engineer is required to state this fact if directly questioned but is not required to volunteer the information otherwise. This opens the door to expert witnesses being trained in subtle ways to avoid being led by the opposing side into being asked directly to reveal information damaging to their attorney's case. Should the legal system be modified to require expert witnesses hired by one party in the trial to produce all relevant information about a case with complete impartiality?