chemist back in the'30s, and has been studied for decades. much is known about its effects. and in mueller's experience, he knows lsd can trigger deadly behavior. somebody jumps out a window or acts out because of the lsd? >> absolutely. yeah. injures themselves or gets in a fight or, yeah, jumps out a window. >> reporter: but the drug itself is not usually deadly. >> an lsd overdose typically isn't going to happen in our experience. and so, our concern at that time is immediately what was ingested? was that the cause of her death? and is there any more out there? >> reporter: even tara's grief-stricken father was perplexed. >> when i heard "acid, " i thought, i've never heard about anybody overdosing from acid. so it seemed really peculiar. i mean, this is some of the things that were running through my mind. >> reporter: and another question, if tara and her friend both took the drug, why did one girl live and the other die? michelle frascone was the lead detective. how do you explain that? >> terrifying. i mean, that is