I’m sorry, but how can you demonstrate that there is no fraud when the identity of people voting is not verified? You simply can not. At best you can say the ballots cast are all for registered voters, but not that they actually cast them.
You compare the signature with what's on the voter record. You check records to see if they passed away recently. Then you can compare addresses and any other personal details. This is more than enough information to strongly verify that the person who voted was who they say.
It's why fraud is rare and why the cases of attempted mass voting fraud are immediately identified (see: Leslie McCrae Dowless)