If you're being interviewed by the Police and accused of committing a criminal offence, it is your legal right not to incriminate yourself. You can choose to remain silent or not say anything that would suggest that you committed the offence.
Though you are not required to incriminate yourself, it is in your best interest to cooperate with the police and share what information you have. Cooperation can help protect individuals from being falsely accused of crimes they did not commit or minimize their sentence if convicted.
When preparing your defence, it is important to mention the facts early in your statement when you have the opportunity. If this information is not mentioned until later on and a Court feels that there was an ulterior motive for withholding these details then they may deem any subsequent defences less believable because of their late inclusion into the story.