The Vampiric Dagger
The last pages of the diary describe how the husband drugged his wife's tea, using the various herbs that Merlin had previously identified within the teacup, along with holy water to protect her body from turning.
The diary then described an ornate dagger, blessed by the temple and used for certain concoctions that required divine energy and ritual. What was supposed to be a tool of healing had been used out of fear, used for a purpose most foul.
The husband had thrust the dagger into his pregnant wife's stomach, piercing his now-undead child and ultimately killing both it and his wife.
The writing had become deranged and almost cryptic, the erratic scribbles flooded the pages, and Merlin couldn't find any value in decoding more than a couple of lines.