How would Slim feel after Lennie killed Curley's wife in 'Of Mice and Men'?

Curley's wife observes that Lennie is "[j]us' like a big baby" (99) and invites him to stroke her soft hair. Lennie begins to feel her hair and likes it very much indeed, which leads him to pet it too hard. Curley's wife begins to struggle, which sends Lennie into a panic. He grabs a hold of her hair and muffles her screams. When she continues to struggle, Lennie grows angry. He shakes her violently, telling her to keep quiet so that George doesn't hear her. Before he knows it, he has broken her neck. She lies dead on the hay. Lennie observes that he has "done a bad thing" (100) and covers her body with hay. He then disappears from the barn with the dead puppy in hand.

Candy comes looking for Lennie in the barn and discovers the body of Curley's wife. He fetches George, who knows exactly what has happened when he sees the body. Candy warns that Curley will lynch Lennie if they don't let him get away. After a sombre exchange in which Candy and George acknowledge that their dream of a farm can't amount to reality anymore, George decides the best course of action. He tells Candy to spread the news of the death to the rest of the men and to pretend that he (George) was never present in the barn. When George leaves, Candy scolds the corpse for being a "God damn tramp" (104).

Candy fetches the men and Curley immediately connects the killing to Lennie. He and Carlson run off to fetch guns. Meanwhile, George and Slim hypothesize that Lennie must have accidentally killed her, in the same way he got in trouble in Weed. George asks Slim whether Lennie might just be locked up and Slim replies that Curley will want to shoot him. Carlson returns and announces that his Luger has been stolen. He blames Lennie for the theft.

As for Slim ... Well.. the events don't surprise George or Slim at all, they are instantly able to determine from a look at Curley's wife that Lennie is the culprit and you see this when Slim sighs and says he guesses they've got to go get Lennie now. (He seems sorry things have worked out this way.)

Slim is the "prince of the ranch."- strong, fair-minded, practical and exceptionally good at what he does. He is highly regarded among men, and his word on any subject is law.

Slim's "authority" means that he gets to decide who deserves justice, and who deserves a little leniency. He's good at reading character, saying "I can tell a mean guy from a mile off" (3.28)—and, unlike some other people in the novel, he's not saying that out of ego. It's just true.

When Slim does lie, he lies for the good of the group or to protect the weak. After Lennie crushes Curley's hand, Slim tells Curley what to do: "I think you got your han' caught in a machine. If you don't tell nobody what happened, we ain't going to. But you jus' tell an' try to get this guy canned and we'll tell ever'body, an' then will you get the laugh" (3.259-260).

This is the kind of lie where you tell your friend that you like her new haircut because you don't want to hurt her feelings: the damage has been done, and now you just have to try to smooth it over until the bangs grow back. As unofficial judge and jury of the ranch, Slim gets to decide who's in the right (Lennie) and what the punishment is (not being able to retaliate).

Slim is the only one who understand what George has done—and why. As the novel's moral center (and possible author avatar), he okays the mercy killing: Never you mind," he says to George: "A guy got to sometimes" (6.96). According to Slim's Man Code, if someone has to die, it's better to do it yourself. You can't let a stranger kill your friends.