zobia , for that very reason I mentioned that if you can provide enough proof .... in my first few comments.
When you have heard it from the horse's mouth about their actions , there is no way they should be protected.
When it comes to total honesty , one has to ensure that they give precise truth and nothing else, I once told a girls family , inquiring about a certain guy, that his very close friends have seen him intimately interacting with girls , but i havnt seen it with my eyes , so if you wish , you can investigate further.
i think it's important to be honest with them- they're asking for your input, so it's your job to give it. i don't think that necessarily means you have to say exactly what you've seen them do but you have to let them know if there is cause for concern. i think it's more hurtful to everyone if you pretend to not know about something, because at some point in time later on it will be made clear that you knew something was going on and didn't do anything about it.