>> those extra ten minutes, da james farren, believed, were significant. >> from savannah's house, tothree and a half, to five minutes, to drive to that location. so, that means she left her house, about ten minutes. if she arrives at helium road in three and a half, to five minutes -- >> plenty of time. >> she has time to kill robin, and then drive back to manhattan street, and arrive at about 10:20. >> the ten minute gap cast doubt on katie's alibi. >> so, really, it is katy's best friend who puts the noose around her? >> absolutely. >> something else was hurting katie, to. if you watch dateline regularly, you know. cell phone data can make, or break, a case. that was, certainly, true in this one. >> at 10:13, katie paying off of an antenna, at the lockney tower. >> which was close to savannah's house. and, also -- to the crime scene. >> when she checked her voice mail, it pinned off the tower. >> so, the ping from katie's phone, that is consistent with your theory that she had committed a murder, and was heading home. >> if it are theory, that's right. >> the motive means an opport