Joshua Key is said to be a US Army deserter who fled to Canada (which, incidentally, has an extradition treaty with the US for deserters and draft dodgers now). He's published a book, The Deserter's Tale, which purports to be an account of atrocities he witnessed while serving in Iraq. An excerpt — very ugly if true — is online at Why I fled George Bush's war.
As a deserter, Key has an obvious interest in justifying himself. So I think these very serious allegations require corroboration before we can safely rely on them. But serious charges of random violence and apparent gang rape demand at least some investigation. Especially as the book is going to have Canadian, Australian, French, German, Dutch, Indian, Italian, Norwegian, Swedish and Japanese editions.
Unfortunately, that sort of investigation is not at all easy. And the US Army presumably has no great interest in risking corroboration. I fear we may never know for sure.