There are times when one has to leave gun in a car unattended out of necessity. If you go out to lunch of dinner after a rifle match 90- miles away from your house, other solutions are impractical. When I have to leave a gun in my car in high-risk locales, I cable tie it to the structure of the trunk.
Reporting through attorney is not always practical. BUT, know the law, and what to say. Something like "I want to report a stolen locked gun case, and by the way, there was a gun in it.
In practice, it is up to him to show the gun was secured. Getting this into the initial police report is critical, and has much more credibility than adding an "oh yeah.... it was in a locked case" after charges are filed.
I have a trigger lock on all guns I am transporting (locked case for high cap rifles). Even a spare gun in the range bag at a match has a trigger lock - surviving theft of a gun is easier, and generally cheaper, than surviving governmental theft of an LTC.