Of what is Oliver's brother suspected in As You Like It? What evidence is there against him?
I think that what you are talking about is the fact that Orlando (Oliver's brother) is suspected of having run off with Celia, the daughter of Duke Senior.
Celia is a really good friend of her cousin, Rosalind. Rosalind is in love with Orlando. Orlando finds out that Oliver is trying to kill him. Because of this, Orlando runs away into the Forest of Arden.
At about the same time, Duke Frederick throws Rosalind out and she goes into the forest as well. Celia goes with her because they are such good friends. Because they all leave at about the same time, Duke Frederick suspects that Orlando has something to do with them leaving.
Duke Frederic's daughter Celia and her cousin Rosalind has been found missing from the dukedom. Oliver's brother, Orlando is suspected to have been gone away in company of Rosanlind and Celia. Hesperia, the princesse's gentlewoman, confesses that she had overheard Celia and Rosalind praising the merits and virtues of Orlando who had overthrown Charles(Duke's wrestler). She belives that wherever they might have gone, Orlando might have accompanied them. This is the evidence aganist Orlando.