Wormtonge’s manipulation

[Silmarien]

here's a quote from 'The King of the Golden Hall'

To slay it(Grima) would be just. But it was not always as it now is. Once it was a man, and did you service in it's fashion.

He also was corrupted by Saruman. But how much corruption was needed is not said. Gandalf has also said this just before

How long since Saruman bought you? What was the promised price? When all the men were dead, you were to pick your share of the treasure, and take the woman you desire?

This seems to imply that he knew there was going to be killing and lots of it. But, as in the movie it's wipe them out, rather than, kill the men, leave the women and treasure as reward to Sarumans "faithful".