Sorry but I have to disagree. An ICU has plenty of witnesses who are all pretty focused on patients and there is no guarantee their recall is perfect as to the comings and goings of a patient's parent.
In this case, the cell phone records were subpoened anyway. Evidence such as security video and cell phone records are far more reliable than witnesses. The Sheriff could not ignore the cell phone triangulation and he didn't.
JMO
http://www.innocenceproject.org/understand/Eyewitness-Misidentification.php
Eyewitness Misidentification
Eyewitness misidentification is the single greatest cause of wrongful convictions nationwide, playing a role in nearly 75% of convictions overturned through DNA testing.
While eyewitness testimony can be persuasive evidence before a judge or jury, 30 years of strong social science research has proven that eyewitness identification is often unreliable. Research shows that the human mind is not like a tape recorder; we neither record events exactly as we see them, nor recall them like a tape that has been rewound. Instead, witness memory is like any other evidence at a crime scene; it must be preserved carefully and retrieved methodically, or it can be contaminated.