While police officers may be careless and overlook technicalities of the way in which the law ought to influence their behaviour, broadly speaking an officer will modify their behaviour if wearing a camera. I'm not familiar with the statistics regarding wrongful doings in the police force, but am aware that a minority of officers commit wrongful deeds. Among these some will certainly be sufficiently self-aware to avoid incriminating themselves.
Yes, police officers who intentionally commit wrongful acts would know how to keep their acts from being recorded by their body cameras. Officers probably do know how to not get caught doing something wrong even in the presence of cameras because they are aware of where the cameras are. The body cameras are no exception to this fact.
There is really no way for police officers to conceal any wrongful acts from their body cameras, as long as their cameras are on and working properly. Yes, a policeman could turn off his body camera and claim that it malfunctioned. However, as long as a police officer is wearing a working body camera, there is no way for that officer to conceal any wrongdoing.
I am going to hope and pray that the police have not figured out how to circumvent the body cameras because we would be right back where we started from. The whole point of the body camera is to hold them accountable and protect them also from false allegations. There is always that small 1% who are there for the wrong reasons and are motivated to do wrong. Let's hope they can weed them out before they destroy the good that the cameras are doing.