What is nicotine? Why is it harmful?

Nicotine is a chemical that is dangerous not because it causes cancer but because it can addict you to cigarettes. As Michael Russell, the father of tobacco harm reduction theory and the developer of nicotine gum, put it in 1976: "People smoke for nicotine but they die from the tar."

Explanation:

it is harmful because you in hail things that the human body should not have in its lungs that being said there are things like metals that are not meant to even be in your body and some of those things can collect in your lungs for a long time if you say vape or smoke so those things will soon lead you to death and the things in vapes and things like that can lead to a thing called popcorn lung which can also lead you to deaths door real soon.

when comparing the cases, what similarities are there in the cases that suggest one person committed these murders?