Rubbish analogy. AK was a minor and as such his parent’s had full responsibility for him.
They knew he was buying weapons, had found them in his room. They should have taken them to the police station not least to prosecute whoever was selling them to a minor (ah but it seems like they may have signed for them at delivery so on sticky ground there).
They knew he had been caught on a bus with a knife and stated to police that he wanted to stab somebody prior to this.
They had sufficient concern to prevent him from going out the previous week.
The morning of the attack, they knew he’d left the house without saying anything after a year of not going out and after preventing him leaving the week before. Why no concern then despite knowing he’d previously gone out with a knife and the father saying he immediately feared his son had carried out the knife attack when he heard about it, so they obviously knew he was a danger to others. Why didn’t they call police and say they had concerns which, is what they should have done, or gone after him. Police could have put a call out to taxi firms and intercepted him. There was a minimum 15 minute window to stop him and save those poor little girls.
Why did his mother try to prevent information about her son being known to support workers? Why is she denying things her husband and other son said she knew about in their evidence?
They knew he was a danger, had weapons and wanted to kill.
They enabled him to carry out his (no words worthy of the evil) crime through their silence and so are complicit.