It would be nice if it were as straightforward as being able to say that law enforcement is "obligated" to make an arrest. Unfortunately, it is rarely that simple.
First of all, law enforcement officers have a great deal of discretion when making an arrest. When an officer responds to a complaint, he is supposed to ascertain the relevant facts and then determine if he has probable cause for an arrest. If he doesn't believe the facts arise to the level of probable cause, he won't make an arrest.
Further, officers usually consider custodial issues to be civil in nature and not criminal. Typically, they will tell you to call your attorney rather than make an arrest. I've been doing criminal and family law for about 15 years and, in that time, I've seen ONE arrest for interference with custody and that occurred when the father fled with the child during a supervised visitation and attempted to take the child to another country by boat.
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