Thank you for your reply
First off, when the police receive a call from anyone about someone with the gun they take it very seriously. When they encounter the described suspect they do not take their word for it, they act in the manner you describe until they satisfy themselves there are no guns and the officers and everyone else are safe. So the conduct you described above is consistent with police street survival and safety tactics.
Once they satisfied themselves that there were no guns and they investigated, they took proper action in releasing him. Is going through this embarrassing, intimidating, abusive, sure it is, but it is not unlawful conduct by the police.
What was unlawful is his wife filing a false report. If the police refused to take action on that, as is their discretion, your son has two options and can execute both of them. First, he can go to the DA and bring them all the evidence and seek to get the DA to file criminal charges against the wife for filing a false police report, which is a criminal offense. The DA has the ultimate and final say as to whether or not any criminal charges will be filed. It is not simply "Her word over his word," because the police investigated and found no gun anywhere around him or on him and there was no evidence of any fight or argument discovered by the officers (if they had found something your son would have been arrested for domestic violence
) and this is basically the officers exercising their discretion to close the matter and take no action at all.
The second option is that your son, in addition to going to the DA, can file a civil suit against the wife for defamation
/slander for her making known false complaints to third parties about him and for intentional infliction of emotional distress and can seek money damages from her for her conduct.
So your son's recourse is against his wife and he needs to get his attorney and take the matter to the courts as a civil action
in addition to the divorce. He also needs to have his attorney file in the divorce to obtain temporary custody and/or visitation of the children and get a court order in place since it seems she is not going to act properly in the best interests of the children.