Was the casting of Alan Rickman as Snape based on the full knowledge of the future of that character?

Question

Casting Alan Rickman (a great actor) in the role of Snape would make a great deal of sense if one considers the depth of the character as exposed by all the books up to the seventh one.

A great example is the deleted scene from the HBP movie:

The still – which does absolutely no justice to Rickman's talent – is on HP Wikia. I'd prefer not to post the links to the video as that might violate copyright.

 

The scene shows the choir singing 'In Noctem` and then Snape looking out at the approaching darkness.

But it seems a mite of an overkill (shades of Alec Guinness here) if one merely needs to portray an somewhat evilly guy from "The Philosopher's Stone" – yes, Rickman played those before (e.g. Die Hard), but still an overkill – and he's been known to turn down blockbuster roles before (he turned down the villain role in 007 movie Goldeneye.

Is there any support for the theory that the casting of Alan Rickman was done based on at least a rough idea of his full story and depth as a character in JKR's mind?

Ideally I'd like an explicit statement from someone involved; but circumstantial evidence based on timelines would also be OK if the former doesn't exist.

Answer 1

From wikipedia:

Severus Snape appears in all eight Harry Potter films, portrayed by British actor Alan Rickman. Rickman was Rowling's personal choice to portray the character. He had conversations with Rowling about his character and is one of the few Harry Potter actors that she spoke to prior to the completion of the book series about the future direction of the character. "He knew very early on that he'd been in love with Lily," said Rowling. "He needed to understand […] where this bitterness towards this boy who's the living example of her preference for another man came from."

Also from a Time article:

Rowling also had a hand in choosing most of the adult cast members. She specifically requested Coltrane. Others, like Richard Harris as Dumbledore, Maggie Smith as Professor McGonagall and Alan Rickman as Professor Snape came straight from a wish list of actors that Rowling provided the producers. She gave Rickman and Coltrane precious bits of information about their characters' futures.

And, from a much later Time article, Alan Rickman is quote as saying:

"Three children have become adults since a phone call with Jo Rowling, containing one small clue, persuaded me that there was more to Snape than an unchanging costume, and that even though only three of the books were out at that time, she held the entire massive but delicate narrative in the surest of hands."

Answer 2

It appears that while Rowling herself knew what was coming, she did not release all of that information to Rickman, just a few pieces. As K-H-W states Rowling did want Rickman to play the part, so she must have envisioned him in this role to the end.

There is a longstanding story that Rowling let Rickman know early on that Snape was not the bad guy or Voldemort henchman in waiting many expected him to be. Before I could even finish my question about this anecdote Rickman jumped in to clarify.

According to Alan Rickman.

"Not true. I don't know who thinks that is true, but it's not true," Rickman says. "She gave me one tiny, little, left of field piece of information that helped me think that he was more complicated and that the story was not going to be as straight down the line as everybody thought. If you remember when I did the first film she'd only written three or four books, so nobody knew where it was really going except her. And its was important for her that I know something, but she only gave me a tiny piece of information which helped me think it was a more ambiguous route." LINK

Rickman adds,

"What I knew was he was a human being and not an automaton and I knew there was some sense of protection for Harry or I worked that out. It was enough to know, I didn't know he was a double agent."

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"Three children have become adults since a phone call with Jo Rowling, containing one small clue, persuaded me that there was more to Snape than an unchanging costume, and that even though only three of the books were out at that time, she held the entire massive but delicate narrative in the surest of hands. quote

Here we see that by book 3, Rickman knew JRK had a plan in store for Snape.

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"She certainly didn't tell me what the end of the story was going to be in any way at all," Rickman said. "No, she gave me one little piece of information, which I always said I would never share with anybody and never have, and never will. It wasn't a plot point, or crucial in any tangible way, but it was crucial to me as a piece of information that made me travel down that road rather than that one or that one or that one." Rowling revealed [on Twitter] what she had told Rickman: "I told Alan what lies behind the word 'Always'." quote

This "Always" was most likely in reference to Snape Loving Lilly, showing that Rowling had planned Snapes story out by book 3, when hiring Rickman.