Seeing a Muslim Purchasing Alcohol

Salams,

Like to know your advice on this. My child saw one Muslim person we know from a Muslim fast food store purchase bottles of beer and brought this to my attention. I came closer and saw the bottles being put inside the bag and asked the cashier if they were soft drinks, but she told me they were beer and even gave me the trade name. This brother is a Muslim he works for a well known Take Away on a main street within a Muslim community and I tried speaking to the manager but they would not give me his contact details. I think the brother suspects that I know about this and that is why he asked why I wanted to contact his manager. Tbh, I just wanted to tell the manager to take care of his employees and keep an eye out on them, without point at anyone, I wanted him to be aware this is going on and that it was not going to help his business if other Muslims found out that one of the men working there is purchasing alcoholic drinks. But as I said they didn't give me his phone number. 

So I have notified some responsible Muslims who will discuss the issue with an Imam. I said to them that I felt responsible that if other younger Muslim may watch him purchasing alcohol they may get encouraged to drink it, but I reminded them that they should try to conceal his sin, so that Allah will cover ours and I did not give them his name, but only the name of the fast food store.

I don't know if I did the right thing. I don't know what will happen.  The sister I spoke to said it was important they knew about it as they would like to speak to him diplomatically about this. I feel confused, because I don't know how the brother will may take it or will understand why this is wrong to do what he's doing. I think he knows we saw him purchase alcohol, but I don't know if he bought those bottles of beer to drink for himself, or for someone else.

Any suggestions from Muslims will be appreciated.

Jazak Allahkhair