design. >> but the tennis shoes were two sizes smaller than the shoe size of their prime suspect, gregg myers. so, again, there was nothing in the bag which linked gregg meyers directly to the murders. >> they were certainly concerned that a murderer could go free unless they did a lot of work to put the case together after that point. >> since the serial number on the shotgun had been ground off, investigators sent the gun to forensic scientist timothy duerr. he knew that scratch marks usually weren't as deep as the original engraving. >> the serial number may only be a few thousandths of an inch, but the compressed metal goes a lot deeper into the metal. >> to restore the serial number, duerr applied an acid solution which only works at one level and goes no deeper. >> it will actually eat away and you can actually burn past the point of compression. it reacts differently between the compressed and uncompressed metal. the compressed being the serial number. >> the acid solution removed the top surface, leaving the bottom, or compressed metal, virtually untouched. >> upon utilizing an the re