An unintended consequence or benefit, depending on how you look at it, of giving your DNA is that it helps solve cold cases and usually for Murder. A few cold cases in the US have been solved by linking familial DNA and then tracing the family tree to people associated with the victim. This is scary in one sense and it is not being used for what you provided it for but does put murderers behind bars. I think the practice has since been halted to share the DNA with crime labs as the question of access is being questioned.
There seems to be some misunderstanding about how this works.
Police have been collecting samples (fingerprints, or perhaps more relevantly blood, semen, etc.) at crime scenes to be investigated for many decades, long before the science of DNA developed to its present state. Some samples collected maybe 40 years ago and stored since then may now be able to give them a DNA profile of the otherwise unknown murderer. They can use this profile to form an autosomal DNA raw data file that can be uploaded to GedMatch. GedMatch results give them a list of potential relatives of the murderer from among the million or more people who have already also uploaded their raw data info to GedMatch. Most of them are probably too distantly related to be of much practical use, but they may be able figure out something from a third cousin or closer match. The closer the relative connection, the easier it becomes for the police to narrow down a list of possible suspects from family trees, and find him (or her) and get an undercover cop to trail the person to eventually get a coffee cup they discard (or tissue or some such thing like that) to test if the suspect is indeed a direct match for the murderer's DNA.
The only thing the police get from using GedMatch is names of the murderer's relatives. This does
not involve GedMatch and the consumer DNA testing companies voluntarily or involuntarily giving away anyone's actual DNA or DNA data (the A, C, G, and T's) to police. The police don't get, don't want, and don't need access to it, and therefore don't need a court order because they're only using GedMatch in the same way as anyone else does -- to trace out exactly how some likely second cousin once removed on another continent is related to you through a common ancestor. I have done that myself. It takes some work, but you certainly don't have to be some kind of highly educated expert in the field. The closest relative will probably never have any idea they unknowingly helped catch a murderer.
It doesn't involve any surreptitious "hacking" or "data breaches" perpetrated by the police investigators, because it doesn't have to, and they don't want or need it. I'm not sure how or why you think this can or would have been stopped. I seriously doubt police are ever going to be told they're not allowed to investigate crimes by collecting samples at crime scenes.
http://www.cbsnews.com/news/genetic-genealogy-tracing-family-trees-to-catch-killers-60-minutes/