Unless we can see the evidence, there is no way to sleuth this case.
I'd like to know if the Ingrams considered anyone else as a perp other than the guy down the street or an unknown stranger stalker. If they have, how did they rule out those people as possible contributors to Morgan's demise. The answer can't be that he would never do a thing like that either.
Keeping in mind we don't know the ex bf's name or where he lives or anything, imo the night Morgan died he'd be the one with the easiest access into the home and her room. She may have even invited him in. That's why I can't stop thinking about wanting to know the circumstances surrounding their breakup and the reason he made himself present at her house again. Was it he who desired to see her again? Could he have cared less which is why he could handle going to help her father but it was she who felt hurt all over again by seeing him?
We know the drugs killed Morgan and that they weren't a build up but one deadly dose. She either took the drugs or someone who gained access to her administered them to her some way.
To me the least likely scenario is that it was a stranger or even the guy down the street. Depending on what the experts say it's more likely the drugs entered her system before she returned home (unless she took them herself). So, if she ingested the drug at 8pm let's say, how long would it take before they killed her?
Someone mentioned Claritin versus Zyrtec earlier. One of the ads Zyrtec uses is that Claritin takes three hours before it provides relief yet Zyrtec begins working within the first hour. How long would it take before the high dose of Elavil would kick in and render one useless? If it's within the first hour, she'd almost have to have had it administered after she got home.
Can this be answered without knowing the exact number of pills or the way the drug entered her body?