if we're talking about crime and the USA, then it legally depends on what state. in most places, there's no legal obligation to report any crimes. there seems to be exceptions. if you want to cross into a moral perspective, then things get more complicated. life has a lot of other plans. maybe you are being blackmailed and can not afford to expose anything. in such situations, it may be wise to keep quiet. other times, you do not want to get involved because it is too much of a hassle. you could be regarded as a callous person for that.
however, if someone's life is in immediate danger due to a situation, i would say morals should always try take priority. you're a human being and you should be compelled to keep others out of danger. unless telling others about the dangerous situation results in negative effects applied onto yourself. you do not want to help others when you will be unable to help yourself. you are told to put your oxygen masks on a plane before helping others
if we're talking other situations such a workplace habits, keeping quiet about those may not be a legal problem. but doing so may result lawsuits, disciplinary action, and/or losing your job.
Answer: Katniss believes that the game makers allowed them to have partners so that they would get closer to the end. Both the tributes needed something to help them survive the game makers believed if they pushed them together with the rule change that they would have to help each other AND there would be more of a blood bath between Cato and peter.
