It would be a pyrrhic victory for you even if you prove it wasn't you that was downloading it. Your name is going to be in court documents associated with prosecution over csam or other illegal materials. This information will be easily found. If you're the first case of it's kind, you will also have to deal with whatever tales the media spins about this. If you're somewhere like Florida, you might end up with your photo next to a label of 'pedophile' being plastered publicly.

A lot of people will simply see the headline, assume you're guilty and treat you as such. And a lot of people are willing to treat those they think are pedophiles very very badly (there was a case recently where a murderer serving life in jail killed his pedophile cellmate) Anyone that knows about this incident will probably never allow you to be around kids unattended, regardless of your innocence. You will be a social pariah.

Innocent until proven guilty had to be enshrined in law because most people will treat you guilty until proven innocent, and they don't have much concern about forgetting the 'proven innocent' bit.