Speed was an expert witness for the defense of O.J. Simpson at the trial for the O. J. Simpson murder case, as well as an expert witness in the Imanishi-Kari case, an affair of alleged scientific misconduct which involved biologist David Baltimore. Much earlier in his career, he was an expert defence witness in the 1966 trial of Ronald Ryan, the last person executed in Australia; however, his evidence that Ryan must have been at least 2.55 metres tall (he was only 1.73 metres) to fire the fatal shot failed to sway the jury.