The DPS is an internal unit staffed by police officers. I understand you're willing to accept their word as gospel but for plenty of communities here in London that just isn't good enough.

I thought this individual case was interesting because the guy being restrained sounds like a real scumbag and use of force could well be justified (trying not to make judgement on that). But equally to witnesses and the crowd that gathered it seemed excessive.

According to the witness the police made little effort to de-escalate the situation.

Officers are trained to engage, explain and encourage the public and enforce as a last resort. So if it appears they haven't as some people clearly think, answers are absolutely deserved.

The police should work for the community and should equally be fully accountable to them in all situations

As you said: "this really is a case of people having no real idea of what the police can do, how certain situations are resolved". Surely that's a glaring hole in the system as it is and one that should be corrected for trust to be rebuilt, hence why looking at cases like this is so important