Victim's laptop is needed by police for a criminal investigation to figure out if the accused has sent emails or not. What is the process to figure out where emails have came from? Will they go through everything on the computer as well?
And yes, they can take an image, or other forensic copy,
but they will probably just take the whole machine.
And if you tamper with it before they take it for examination
such as by clearing your browser history, cookies, cache, temp files, etc,
or by deleting stuff (which, let me tell you, is dead easy to recover regardless),
then that can be a problem for you later.