So I have been looking at this completely wrong. Because the girls were found last but killed first. I have always thought that Uhon was a planned target and the girls were unfortunate causalities. But it looks like the girls had something PG wanted so bad he killed for it. And UJ was the unfortunate causality. I'm going to need process that for a bit.
I agree with Elainera that this this all somehow tied to getting a vehicle for some reason - to get away, to sell for drugs, to pay someone back, something.
And I think he expected to be able to do it with no resistance, possibly picked people he thought he could get to not resist, and he didn't expect resistance and so panicked.
I can see how it could have been what you said - the bolded above (though I can also see where Uhon was a total afterthought in panic after killing the girls)
I could see him intending to steal the car (and perhaps drugs) from the girls if he were in a frenzied/ampped up state.
With that possibly simply for money for drugs or something, but also possibly somehow related to wanting to get to Uhon's for whatever reason - revenge, to get his car, something. Perhaps even intending to leave Alex's car near Uhon's trying to implicate them somehow.
[I can also see this component totally being eliminated and Uhon truly not coming into play until after]
The girls resist, so he "has" to kill them.
He also knows if he didn't kill them, he knew he'd have to be far, far away and not return or else they would be able to ID him and the whole thing would be up anyway.
So then instead of taking their car and either getting out of dodge or going to Uhon's for something pre-planned, then Pierre's really in a state, plus is desperate for a car.
Now he has two dead girls, knows at least some communication will tie them to him, and he still hasn't gotten the vehicle, he's already frenzied, so now he's basically unhinged.
He runs in his frenetic state to Uhon's, again tries to get a car, again gets resistance, and he kills Uhon, since now he
really, really needs to get away!
Whether he was intending to target Uhon from the get go - or to simply go there and go after Uhon's car from the get go - I don't think Uhon was a fluke as he surely had
someone he knew who lived closer to the river, unless perhaps none of those people had a car.
Most of me thinks he had Uhon on his radar all along, but a piece of me could see it being his flat out panic after killing the girls and that just being the first person/place he thought of where he might be able to get a car (presumably with no resistance)