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Is DNA enough?

In recent years, advances in DNA and other forensic technologies have helped solve crimes, especially in cold case murders.
I often tell people that forensics has advanced more in the past two or three years than in the previous twenty years.
That being said, it’s still up to the detective investigating a case to be diligent in their investigation. Just because DNA or a fingerprint is found at the crime scene, even on the victim, it doesn’t mean the contributor is the person who committed the crime. It’s up to the detective to figure out how the evidence could have been at the scene other than by the suspect. There will never be a technology that replaces good police work. Sometimes inexperienced detectives think the crime lab can do all the work for them. That is a fatal mistake.
In sex crimes, this is especially important.
Allegations of inter-family sexual abuse where a few spermatozoa were found on a child’s underwear are a particular problem.
An act as simple as doing laundry can transfer DNA when no crime was committed. Evidence can survive going through the wash. There must be corroborating evidence (such as disclosures by the victim) before one can be sure how the evidence got there.
When I trained young detectives, I told them to think of any way the evidence could have been deposited other than by the commission of the crime. Then go and find out why that couldn’t have happened.
When I was a young Sex Crimes detective, I investigated a case where an older woman was raped in her home. A fingerprint was developed on a phone book just inside her door in processing the scene. It was matched to a suspect. I brought the suspect in.
“Remember the time you stopped by this house to borrow the phone book?” I asked.
“I never borrowed a phone book!” the suspect said.
“Well then, you used to deliver phone books to that neighborhood!” I accused.
“I’ve never delivered phone books!” the suspect told me.
Thank you very much. I just eliminated the only two ways his fingerprint could have gotten on the phonebook, other than having committed the crime. I didn’t even need a confession.
He pled guilty before trial.
Don’t rely on forensics to solve the case. They’re a great tool, but they don’t replace good detective work.

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