Imagine a crime scene where someone has been poisoned. What are a few of the methods and techniques used by detectives to evaluate the scene?What...

First of all let me address the concept of
“nothing-buttery” which you mention in the detail section of your question.  This is a
philosophy of removing God, spirituality, miracles and so forth, and viewing the world
only in terms of reality, nature and science.

While it is
true that crime scene analysis employs the scientific method and objective evaluation of
evidence, there is also a less-than-scientific approach that allows a seasoned detective
to get an idea from components of the scene, the life style and even likely emotions of
the victim.  There may be indicators of the activity and intent of the perpetrator.  So
crime scene analysis does not rely entirely on the “nothing-buttery”
philosophy.

In terms of a crime scene, it is necessary for
the detective to seek evidence and then have that evidence tested in a scientifically
provable and reproducible manner.  Such analysis would apply to fingerprints and
DNA.

In addition to collecting hard evidence and
application of solid scientific principles, the detective might also engage in more
speculative analysis.  Such analysis might include, for instance, an assessment of
emotions going on during the crime based on the degree of scene disruption from a fight,
or a pattern of excessive wounds on the body and therefore overkill, or evaluation of
personal effects at the scene to establish the life style and personality of the
victim.

Thus, detectives might arrive at conclusions about
the crime using the applications of life experience and common sense, an not always rely
on the scientific method, per se.

A newer field of crime
and crime scene analysis relies on a mixture of science, psychology, crime investigation
experience and life experience and common sense.  It is called behavioral analysis. 
Experts in this field (most notably the FBI’s Behavioral Analysis Unit in Quantico, VA)
are adept at gleaning information about a perpetrator from analysis of the scene and the
nature of the crime itself.

The scene of poisoning may
harbor evidence of the source of poisoning (e.g. a glass with poison residue and
fingerprints).  There may be an indication of the manor of death (natural, accident,
homicide or suicide) such as a suicide note.  A poisoning scene that could indicate
accidental death would be a body found in a known drug “shooting gallery” with a needle
still stuck in the arm.

In summary, death scene analysis
requires overall assessment of circumstances based on survey of the scene by an
experienced and world-wise detective.  Theories are then solidified and supported or
perhaps later changed after careful collection of evidence and scientific examination
thereof.

In the case of homicide, the ultimate task of
detectives and crime scene scientists is presentation of his information to a jury so
they can decide on the guilt or innocence of the defendant.