Shulchan Aruch/Yoreh Deah/375
Seif 1: From when does the period of mourning begin? From when he is buried and the filling of the grave with dust is finished, immediately the period of mourning begins and he wraps his head, but he does not take off his shoes until he arrives at his home. And now the practice is to take off shoes immediately after the closing of the burial slab as is [discussed] in Siman 376. Gloss: If he thought that the grave was closed and began to mourn and afterwards he it became known to him that there was a mistake, he returns and begins mourning anew.
Seif 2: For whomever it is their custom to send the deceased to another city in order to bury him and they don’t know when he will be burried, from the time when they turn their faces away from accompanying, they begin to count shiva and shloshim and they begin to mourn. And those who go with him (i.e. the deceased) count from when he is buried. And if the senior member of the family goes with him, even those who are here (i.e. who stay in the city) do not count until he is buried. And the senior member of the family is the one on whom the household relies, and they are all drawn after him, whether he is a brother, whether he is a son not yet at the age of majority. And there is one who says that he must be at least 13 years old.
Seif 7: One who drowned in [a body of] water that had an end [i.e. with reasonably close shores], or about whom a rumor went out that thieves killed him or a wild animal dragged him, from when do we count (i.e. shiva and shloshim)? From when they despair of searching (lit. requesting). If they found him dismembered (lit. limbs by limbs) and they identify him by signs on his body they do not count until they find his head and the majority of his body or they despair of searching. And if they find him after they had despaired of finding him, the relatives do not need to go back and mourn; but the sons, if they were present at the moment he was found, they mourn on the same day, since it is not any less significant than the gathering his father’s bones. But if they are not there but they heard after the day had passed, they do not need to mourn. Gloss: If they sent their deceased to another city in which case the law is to start mourning when they turn around, and they began to count the period of mourning, and afterwards, the deceased was captured and it was not possible to be bury him for a long time, they do not need to stop their mourning and they do not need to go back and mourn afterwards, for since their rule is to begin immediately, they do not need to stop.