I am trying to remember a case where the suspect fully cooperated with LE from day one and kept continuing to do so. Most of the ones I can remember may have done an initial interview and next thing we know they had lawyered up pretty quickly.
IMO
Because it came to mind and it has been brought up....
Susan Smith never even got angry up until the Agent accused her of murdering her children. Even after that she was still cooperative, considering. She took several polygraphs (never passed one especially on "Do you know where your children are") just didn't tell them the truth. But she never refused to be interviewed by LE.
A few other interesting notes about Susan Smith's case:
The Sheriff also defended Susan very strongly for the first couple of days. It was only after the FBI and other LE came in that they began to see the inconsistencies and the Sheriff began to see it. The "crying without tears" was of concern as were slight inconsistencies.
There was also a cop who intentionally got quite close to Susan Smith, to gain her trust.
They were concerned if they pushed her too hard she might commit suicide.
They intentionally built up the media frenzy to apply pressure to Susan. Press conferences they held were specifically scripted to do so.
They actually even planned to make a fake newspaper with an article about a woman who killed her children, served a short jail sentence, then got out and married a wealthy doctor. To try and convince her to confess so she could have a better life. But that wasn't needed.
It was that original Sheriff that so defended her, that knew some of her family... who ended up getting her to confess. Just simply during another interrogation after 9 days... By praying with her.
It was also noted that Susan submerging them in water was "womb-like" and that this is common in mother's who murder their children. Submerging them in water or wrapping them in plastic. Also that they are found within ten miles of their home.
Susan Smith's case was really quite... advanced for it's time. Considering the investigative avenues that were not yet available to them, they got pretty creative.
http://www.trutv.com/library/crime/notorious_murders/famous/smith/index_1.html