josh-attacked-dnaJosh was knocked unconscious at a party at his house. Witnesses say he was hit over the head with a cricket bat by someone who then fled the scene.

Detective Jess Hodges

He was taken to hospital but died before the police officer could interview him.

Detective Jess removes the bat and Josh’s blood-covered shirt from the crime scene. She sends these items off to the Institute of Environmental Science and Research laboratory (ESR) for  DNA analysis. She hopes the results may provide investigative leads and/or eliminate people from her inquiries.


The results are back from ESR.

ESR scientists have examined Josh’s shirt and the cricket bat and found DNA from two other people (some on the shirt and some on the bat). The scientists have generated DNA profiles from these samples.

To find out who the unidentified DNA profiles might belong to, ESR scientists have compared the profiles against the National DNA Profile Databank and the Temporary Databank. Together, these Databanks contain DNA profiles of people convicted or charged with specified crimes, as well as DNA profiles of other people who have agreed to have their profiles added to it.

The profile of a man named Mike, whose profile is on the Databank, matches the DNA profile from the shirt.  However, the profile from the DNA on the bat does not match with any of the Databank profiles.

As well as Mike, Detective Jess has identified two more persons of interest – Chris and Sam. They were at the party.  She sets out to find them all and talk to them.



Chris is Josh’s best mate. He was at the party but says he did not hit Josh. However Detective Jess has found some other information that makes her suspect Chris, so she asks if he will provide a DNA sample by consent, so that she can use the DNA analysis results as a lead in the case or to discount Chris from her inquiries. Chris agrees, as he wants to be cleared of suspicion.

Detective Jess  also asks Chris if he will agree for his DNA sample once it is analysed, to be loaded on the DNA Profile Databank and compared to past unsolved crimes. Chris agrees.  

When the results come back from ESR, it turns out Chris had nothing to do with Josh’s death. But his DNA profile did link to a crime scene profile from a shoplifting. Chris is now 25 years old but remembers that, when he was 14, he stole a chocolate bar from a dairy. (See what the law says about Police keeping DNA samples and profiles).

What do you think about keeping crime scene profiles for low level offences? Go to the “Have Your Say” button on the Navigation Bar. 



Sam was at the party. She is Josh’s ex-girlfriend but says she still got on well with Josh.  

As Detective Jess talks with Sam, Sam wipes the tears away from her face with a tissue – she is obviously very upset about Josh’s death.  Sam says she hates cricket, so did not go anywhere near the cricket bat. As she left the party early, she only found out about the attack the next day. 

However, Detective Jess’s further investigations reveal that Sam’s story does not add up. Detective Jess believes there is enough information for her to request Sam to provide a DNA sample.  Sam is offended by the request and refuses to give one.  She is adamant there is no point in taking a DNA sample from her as she is innocent. 

Detective Jess has the option to apply to a Judge to make Sam give a sample. (See When and how police can take DNA samples). Or, instead, she could send off for analysis the tissue that Sam threw into the rubbish bin after she had wiped her face.  

New Zealand Police do not usually do this, but there is no law against it.   

Do you think Police should be able to collect and analyse discarded items from suspects? Go to the “Have Your Say” button on the Navigation Bar. 



Detective Jess tracks Mike down at the gym where he is working out.  Mike’s DNA profile is on the  DNA Profile Databank  because he was convicted of committing a burglary 15 years ago. He has not committed any other offences since then.

Mike tells Detective Jess it must be a mistake that his DNA has showed up on Josh’s shirt as he has never heard of Josh and was at home with his family on the night of the attack. Detective Jess shows Mike a  photo of Josh. Mike then realises that he has chatted with a guy at the gym who looked like Josh and even moved some of his gear when they were in the changing room, the day before the attack. Mike thinks maybe this is why his DNA was found on Josh’s shirt. 

The latest scientific research shows that people leave small amounts of DNA everywhere. Forensic scientists only need a tiny sample of DNA in order to analyse it and produce a  DNA profile. 

Mike would never have come to Detective Jess’s attention if his DNA profile had not been on the DNA Profile Databank. There is no other evidence linking Mike with the crime and none of the witnesses recall seeing anyone of Mike’s description at the party.

What do you think about someone’s DNA profile remaining on the DNA Profile Databank, even if they have not committed another offence for a long time. Go to the “Have Your Say” button on the Navigation Bar.