Describe the attack on Mrs. Joe in Chapter 13. What weapon was used? What does Pip imply about the weapon?

Someone took an old leg iron (a convict's) and hit Mrs. Joe in the back of the head with it.  It seems to be the one that the first convict filed off the day that Pip went to the graveyard and gave him the file.  Joe examines it and says that it was filed a long time ago. 

Pip seems to believe this leg iron is one in the same, yet he does not think that the convict was at fault.  He is suspicious of both Orlick and the man stirring his drink with the file.  Orlick was seen in town after the attack, and even walked back with them towards Joe's house.  The other man with the file is somehow related, but Pip does not yet know how he's related.