I need some help.

I've a few questions I could not understand and I'm hoping anyone of you can help me.

Pleas read these two sentences:

1) He is not legally dead.

2) He is not dead legally.

Are the two sentences similar in meaning? They don't sound the same to me.

My opinion: 1) According to the law, he's not dead. He might be lost and untraced but he might not be dead. But because he's not found or seen, according to the law, he's pronounced dead.

2) The way he died is not legal.

Are my views correct? I would like to listen yours. Thanks.

And, what are the functions of legally? Are they adverbs? If they are, then why is 'It is heavily raining' incorrect (I know it's incorrect, I just don't know why) ?

Last question:

1) He is thrown into the water.

2) He is thrown in water.

Which sentence is correct? The formal or the latter?

Thanks a lot.