Ritual

When Tom, known as Lord Voldemort, got access to Black family library, thanks to Walbuga generosity, he was closest to be happy. Knowledge is a power and he craved for power most.

During his search over most dark magic and rituals, he found a ritual, that can be used only by Blacks. At first, he discarded it. No matter how deep in a dark he ready to dive, fucking up with natural order of time is always not a good idea.

Years later, after his first death and more than 13 years of surviving with no body, thanks to soul magic and hocruxes, he found himself almost ready to mess with it.

Multiple encounters with a Potter boy cut dipper into his self preservation and he found himself thinking about details.

When he found out that some of his hocruxes are missing and Potter-boy just stole another one from Gringotts - he was moving forward with it.

Of course he did not use it as it has been described originally. He got original idea, that focused on Black family magic, modified ritual to anchor it around his own body and set time anchor to first meeting with Bellatrix Black.

So he was pretty sure, that in unlikely case of his death, charged ritual would burn Bellatrix body, soul and magic to throw her memories back in time, where he will have to only read them and adjust his plans accordingly.

He was pretty sure that this failsafe would not be needed, but he was slytherin and slytherin always have second and third plans , if they are cunning.