Follow the path deeper into the Iron Tomb and you will come upon your first Death Shard. When damaging the Shards groups of Putrid Ravagers will spawn at certain intervals. There will a total of four separate spawns of these minions and if they are not handled each time they spawn before the Shard is damaged more they can overwhelm a group easily. It is highly recommended that you wait for two sets of these to spawn and kill them all off before finishing killing the Death Shard.
Follow the path ahead as it loops back around and heads south. The next large room you find will have the second Death Shard in it. The final Death Shard is in one of the two rooms that can be used to access the top balcony that the dungeon's final boss resides on. The room that is on the western side of the map contains the Shard. If you choose the wrong path simply walk back down on the opposite side to access the room.