"It's an inexact science." We've heard that phrase often. But, how often have we heard it in reference to DNA? Usually, we hear it more in terms of how it identifies a particular suspect with astronomically-high odds, such as, 'one-in-a-million'. In other words, it must be him because mathematically, it couldn't possibly be anyone else.
Consider the very bad luck of our suspect in today's story:
- A murder was committed.
- The suspect's DNA was found on tape used to gag the victim.
- Based on this evidence, he was promptly arrested.
Now, factor in the very good luck of our suspect in today's story:
- He had an alibi.
- He was able to prove it beyond all doubt (i.e, it wasn't his mother claiming that he'd been with her the entire time – he was in a hospital).
In fact, he was nowhere near the scene at the time of the murder; nor was he ever at the scene. Yet, he spent five months in jail before he was eventually exonerated.
This appears to be a bizarre case of transference.
Furthermore, DNA is not necessarily like snowflakes; sometimes, two samples are identical (at least within the range that law-enforcement would feel comfortable arresting and prosecuting a suspect).
The moral of this story? We rely on science; but sometimes, science must also rely on us.