Unfortunately not a lab test, I saw this on Frontline recently and it was very disturbing to see that confessions could be so easily had: http://www.pbs.org/wgbh/pages/frontline/the-confessions/etc/... Essentially, the story involves these sailors individually confessing to a crime (and allegedly tailoring their confessions to the investigator's words) when they were implicated by someone already being interrogated.…
http://en.wikipedia.org/wiki/West_Memphis_Three
Who were jailed partly because of a police-coerced confession from one of the three. They are still in prison, but apparently close to getting a re-trial.
The case was made famous by the excellent HBO documentary 'Paradise Lost' - which is a must see:
http://en.wikipedia.org/wiki/Paradise_Lost:_The_Child_Murder...
They are lucky because their case has a high-profile because of the film - but there must be many, many other innocent people in prisons because of false confessions.
For example, many people believe that Cameron Todd Willingham, executed in Texas, was also innocent (he was also the subject of a Frontline story:
http://video.pbs.org/video/1618590505/
and a feature in the New Yorker:
http://www.newyorker.com/reporting/2009/09/07/090907fa_fact_...