I'm struggling with how they can blame the police for something going missing from the house that the police hadn't classed as crucial evidence.
From what I can make out, Masipa was pissed off with the police. It was their responsibility to lock down the scene, and it stayed locked down for a long time. Everything that was removed from the house should have been logged and should have gone on the inventory.
Anything that was not on the inventory should have remained in the house. So basically, everything was in one of two police-controlled places; the evidence store or in the house. When Aimee packed a bag for Oscar, she did so with a police officer watching her. We know that things were lax during that time, as she removed Reeva's handbag. It was the police responsibility to spot that and control it.
The cable is neither on the inventory nor in the house during the time that the site was in police control, so she wants to know why that is. We know it wasn't there while the house was still under police control, because Roux said he'd looked for it there.
I agree that Nel shouldn't have used this as evidence without knowing where it was and that it had been properly logged and measured.