As far as I have learned. Generally speaking, when someone dies, it is necessary to keep his body intact where possible. When a person first dies, and in that in between stage, that body needs to be treated with respect even to the point of not looking at it directly. When a Jewish person dies, his body his supposed to be washed in a mikva or something like that. The person doing that is told to ask the body permission each time he wants to move a limb or anything like that. If for any reason the burial cannot be done that day, it cannot be left alone in the coffin. Someone needs to be with it. And you're not supposed to talk about the person even..but pray and sing psalms.
Why is this? Because what if it someone were alive? Would it be right to stare at him? Would it be right to just move his limbs without asking his permission? etc etc...We were made in Gd's image..and therefore, any dead body has to be treated with respect.
Now, what does this have to do with autopsies? Well, you are cutting into a freshly dead body...don't think it's right just do it.
But in reality, if it is not needed, autopsies should not be done. If it is in the case of solving a murder and it will save lives, in my opinoin, it should be necessary to do.