Yes, sad and terrible as their actions were, it wasn't as if they knew he'd been stabbed and with hands covered in blood, handcuffed him.
As far as i can see, they had no idea he'd been stabbed, i believe the injuries were internal, so very little external evidence of being stabbed.
The Police get told lots of things by people they deal with.... in this case they got it terribly wrong.
The inquiry will show what needs to change in training and lessons learned.
What is deliberate though, is the 'right wing exploiting this for their own twisted ends, as historically they always have done.