You need to do your job and let the company handle this when he gets caught. they always do eventually.
I would be on your side if it was a severe safety issue or a matter of life or death.
to give you an example , one of our drivers confided to his best friend that he was going to bring a gun to work and kill a couple bosses and some drivers . this driver asked me what he should do.
I asked him if he thought his best friend was just messing around or did he think he was being serious. he told me his friend has been drinking a lot and doing drugs and thought he was serious.
I told him if he did not report him I would. he reported him and the driver was drug tested and came up dirty and was terminated. this driver later had a breakdown and was being treated for mental issues.
It was the right thing to do and may have prevented a tragedy .