Sometimes, it is very hard to say it out something that you want to say, it is either you have made a promise to somebody or you need to think twice before u said it out as when u said it out, some people may just back stab you.
They may think that you donot know about that,but actually you know, and you just feel that you do not want to say it out to avoid contravention.
Some people may suspicious on you as they think that you have known too much think and they will try to keep secrets from you.

However, instead of asking the person itself, your friends just keep suspicious on you but actually you have done nothing. These type of situation, may make the 'suspected person' feel uncomfortable with her/his surrounding circumstances in which at first the person may have willing to talk to you as he/she is comfortable and believe on the friends ,but once they backstab/talked behind her/him and she/he knows it then dont expect that this person will talk everything.

In order to make the 'suspected person' talk, the friends must at first believe/ trust her, dont just keep some suspicious eyes on her/him and dont always be too easy to have mood swings.
Haya, dont know what to say.
It is like it is easy to say it out but it is not easy to get it done.