Originally posted by Peter X
She mustn't be very close to her sister if she didn't know who the sister's husband was. Also, if she knew her sister's address, she would know the husband's address, unless they didn't live together. Perhaps there is some other explanation.
But that's precisely why the solution ISN'T "it's the sister's husband!", if that was the solution, of course she'd know who he was!
Look, he comes to the funeral of the mother, right? Therefore, he heard about her death somehow, and knew the MOTHER well enough to attend her funeral.
Well, whoever told him about the mother's death is likely to say to him "You remember (mother's) funeral? Well, you wouldn't believe what happened - her daughter was murdered!"
Even if he doesn't know the daughters at all, it's quite likely that he will go to the 2nd funeral to show support for the family of the mother, who he DID know, who are going through such a terrible time with two deaths in the family.