It's not the ability to develop electronic digital keys...
...that has the cops mystified, it's that the crimes are only able to disable the alarm and open the passenger's door. They can't unlock the ignition nor start the car so more than likely they've developed some cheap tool that sends a default signal to disable the alarm and unlock the pass door but nothing more. Real thieves would have the good stuff and actually steal the car not the contents. Thus these are likely to be amateurs such as teens or drug addicts without the resources to chop-shop the vehicles. They might have modded a remote control garage door opener?