He kept the hair because serial killers are supposed to be trophy keepers. This is TV received wisdom -- I have no idea about real life.
The Minearverse 3: The Network Is a Harsh Mistress
[NAFDA] "There will be an occasional happy, so that it might be crushed under the boot of the writer." From Zorro to Angel (including Wonderfalls and The Inside), this is where Buffistas come to anoint themselves in the bloodbath.
But he wasn't a serial killer in his mind, was he? He was always killing the same person, and it seems backward to keep the parts of the victims that specifically weren't Brandt.
I don't know what most (TV) serial killers think of what they're doing. However, the trophy-keeping (and subsequent discovery by investigators) is standard enough (and perhaps groundless enough) that I don't think it bears dissection.
Do serial killers ever think of themselves as serial killers rather than avengers or something? At least on TV killing mommy over and over seems one of their favourites. Though keeping the hair is a puzzle as you say. Maybe he just liked it.
I think that gets over-dramatized a bit in fiction. A LOT of them just seem to do it for sexual thrills and the sense of godlike power ending another life gives them.
edit: So, not terribly different from Detective Strong's situation.
Wikipedia lists a number of motives:
- Visionary (rarer than you'd think from fiction)
- Power/control
- Hedonistic
- Mission-oriented
- Gain-oriented
Further reading: The Aetiology of Serial Murder: Towards an Integrated Model
He kept the hair because serial killers are supposed to be trophy keepers. This is TV received wisdom -- I have no idea about real life.
Yep. I'd say it's more about having evidence to find than about Strong's psyche.
Maybe he was split, part of him wanted to be the good cop, holding onto evidence of his own crimes.
I just thought he was cutting the hair and spilling the cologne on them so that they would look and smell more like Brandt, since he was building to do that deed to him.
I think the question is more "why keep the hair?"
I think it's because he'd be laughed out of the serial club without them.