constable darryl lunsford decides to check the trunk for drugs. it will be the final act of his life. >> what? >> how about this here? >> do what? >> the suspects stab constable lunsford as they struggle for his .357 magnum and shoot him and run. they might have gotten away with murder but a video camera in lunsford's own patrol car videotapes his own death. when the case comes to trial, the video is condemning evidence that leads to the conviction of all three defendants. not only that, but the darryl lunsford case and cases like it, convince police departments across the country to install video cameras in patrol cars. jim is a texas prosecutor who trains police on the use of mobile video systems. >> there's no one involved in the criminal justice process that does not believe in the videotaping, whether it be defense, prosecution, police officers, judges, because it gathers truth. and that's what court in the courtroom is all about. >> today, a decade after lunsford's death, hundreds of police forces use cruiser cam systems. they come at a cost