No Rav is needed to say that if there is danger, you must take action.
No Rav is needed to say that if there is no danger, you must not report anyone about anything.
A Rav is needed to define the situation – which is difficult, because it is all based on your perception and conclusions. You need a reliable competent Rav to judge how to classify this case, and follow the psak. The Rav will tell you whether your evidence is enough to constitute safek sakanah, vadai sakanah or no sakanah.
Not every situation warrants reporting to the authorities. If you have a way of dealing with it which doesn’t involve mesirah, you probably are not permitted to report. If that involves you getting involved personally, then לא תעמוד על דם רעך will obligate that, and mesirah will still be forbidden.
Don’t take chances with other people’s lives and do nothing.
Don’t take chances with other peope’s lives and report them to the authorities.
Ask a Rav.