Relevance of Information
During the dispatchers' questioning, few of the guilty 911 callers actually lied unless forced to. Most of them deceived by omission, rather than commission. In lieu of offering the complete truth, such as I did it, many provided rambling information, instead of concise points; confusing, rather than clear, details; and extraneous information, instead of relevant facts. These details, although, irrelevant to the dispatchers' questions, frequently related to the criminal act. People who provide more information than necessary may be attempting to convince someone of a deceptive story, rather than simply conveying truthful information. (4) In this regard, investigators must listen carefully to the complete call because the caller may have provided information that reveals vital clues to the homicide.
http://www.fbi.gov/publications/leb/2008/june2008/june2008leb.htm#page22