Burning the national flag is not illegal in Norway (since 2008), however, the police say they will refer this case to the police attorney who will decide on charges.
To quote the police: “We have spoken to the people involved and told them this action is very inappropriate, and people find it offensive. (…) Our [police] lawyer will be looking into the case to see what we can do”
So, it seems the police now have the authority to prosecute purely based on morals.
It seems that the police have discovered that you cannot charge people with a non-crime, so they’ve decided to wait until a citizen reports them.