When I made the Murder squad, I had already had my new work clothes […] hanging in my wardrobe for almost a year. (1.18)
Rob subscribes to the strategy of "dress for the job you want, not the job you have." So he dresses like a murder detective, which in this case involves blue pinstripes and cashmere scarves. Who knew murder detectives were so cuddly?
[Cassie] wasn't dressed like a Murder detective. […] She was wearing combat trousers and a wine-colored woolen sweater with sleeves that came down past her wrists, and clunky runners. (1.28, 1.29)
Wait, are you saying that Cassie got the job maybe—gasp—based on actual skills and not on how she looked? No, that can't be true.
"Everything she's wearing is blue and white, right down to the hair elastics. This kid coordinated." (2.76)
Katy is one of those murder victims that is just perfect for the media—she's a young girl and she dresses well. Her color-coordination speaks to her personality type, too, though. She wants to be a dancer and she takes care of her appearance. A girl who comes from an abusive household might be more likely to look like a total mess.
[Damien] looked like the type who was accustomed to being taken care of by women. (3.54)
Rob is being a little judgmental in his initial assessment of Damien, but he's actually right in a roundabout way. Damien is this type, but it goes a little further; he's not just taken care of by women, he's manipulated by a young woman into doing her bidding.
"We were wary of them, but I think that was mainly because of their image, not because they ever did anything to us." (5.27)
It seems like we shouldn't judge a teenager by his t-shirt, but Devlin and his friends turn out to actually be reprehensible little snots, so the moral actually is not to trust anyone in a Metallica tee.
Katy Devlin was naked under the merciless fluorescent lights and too small for the table, and she looked somehow deader than she had the previous day. (5.67)
This is one of the saddest images of the novel, as the girl who was once a well-dressed dancer is now just a cut open corpse. Not that anyone should ever be murdered, but it's exceptionally gruesome when it's a child, which is why Rob notes that she appears "too small for the table."
One of the photos—Rosalind's anguished, upturned profile, an unflattering shot of me with my mouth open—made it onto the front page of a tabloid the next morning. (9.15)
Police have to watch how they appear to the media. We're surprised this photos doesn't come back to bite Rob in the butt later on after Rosalind starts lying about their relationship.
"I still keep her bedroom the way she left it." (10.143)
By keeping things the same, Jamie's mother keeps her daughter alive. If she were to change the way her daughter's room looks, it would be like changing her memories of her daughter, or letting a piece of her go.
The year I was twelve, I was a big kid. […] I felt monstrous and lost: my own body had betrayed me. (18.130)
Rob looked different from the other kids his age, and it made him uncomfortable.
At certain angles you could see a fuzz of fair, pathetic stubble on [Damien's] chin. (23.5)
We're not sure how stubble can be "pathetic," but Rob thinks it is. This says more about Rob, and how he views other people superficially, than it does about Damien (who is pathetic, but not because of his facial hair).