I don't know enough about Brian Deer to talk about him specifically, but I have to take issue with dittany's (and other's) points about journalists being "objective".
Some journalism is - and always ought to be - objective, eg straightforward news reporting. But one of the strengths of the media is its campaigning role and many of the best journalists have not been "objective" in that sense - see Paul Foot, for example, whose work was crucial in overturning miscarriages of justice such as the Birmingham Six case.
Similarly, when newspapers uncover criminal wrongdoing, the news report will usually state that the evidence collected has been handed over to the police. The newspaper is, I suppose, in a sense the "accuser" in this case. I think such behaviour is entirely justifiable.