i'm detective barry cherowitz, and with me is ralph welch. >> so, ralph welch tells detective barry cherowitz the son the man who turned in that .38 caliber revolver. >> so, we went in, and he told me the story how it happened and who all was there. >> so police get ralph welch talking. and remember, he's a teenager talking to cops. and he spills it all. >> he told you the story about what? about how what happened? >> he told me how they did it. >> how they did what? >> killed gregg smart. >> ralph welch tells police about learning of three teenage boys who went to gregg smart's house that night with the intent to murder him. these are the thr boys that welsh names in that interview. billy flynn, pete randall, and vance aka j.r. lattime. it's startling was they're just high school kids. lattime supposedly waited in the getaway car. >> and so they went there and they broke into the place. and they set it up to make it look like a burglary. and i guess the guy tried to run or something. and they grabbed him and they threw his dog in the cellar. pete said he held the guy's head while bill shot h

. >> reporter: he tells police that his son's friend, a teenager by the name of ralph welch tells him his gun may have been used to kill greg. >> tests show that that gun is the weapon that killed greg smart. >> reporter: that very same day, police bring in ralph welch for a videotaped interview. >> okay. it's june 10th, and it's 15:24 hours by my watch. i'm detective barry cherowitz. >> reporter: he tells about a secret conversation he had with the son of the man who turned in the gun. >> he told me the story how it happened. >> he told you the story about how what happened. >> he told me how they did it. >> how they did what? >> killed greg smart. >> reporter: welch says he learned that three high school boys. billy flinn, pete randall and vance went to greg smart's house that night. flinn and randall went inside. lattime and another boy waited in the get away car. >> they broke into the place. then they set it up to make it look like a burglary. i guess the guy tried to run or something. they grabbed him. they threw his dog in the cellar. they held the guys head and shot him. >> re