At what point do you need a
criminal defense lawyer?

BEFORE charges are filed.  If you learn or
suspect that someone is accusing you of a
criminal act, obtaining a lawyer could
reduce the chances of charges being filed.  
The lawyer can start the process of
obtaining and preserving evidence that
could be used on your behalf should
charges be filed.

BEFORE you consent to an interview with
law enforcement officers
(or allow them to
give you a lie detector test).    A lawyer can
help determine what role you have in an
investigation, advise you of your options
and rights, and reduce the chances of
charges being filed.

BEFORE you are arrested.  If you become
aware that there is a warrant for your
arrest, a lawyer can assist you with
arranging bail, or reducing bond, if
necessary, and keep your period of
confinement as brief as possible after
turning yourself in.  

If you were not afforded the opportunities
mentioned above, you should employ a
lawyer
IMMEDIATELY after your arrest.  
Some of the advantages are the possibility
of bond reduction, assisting in arranging
bail, early evidence gathering and,  if it is a
felony charge, to provide favorable
evidence to the grand jury to avoid being
indicted.