Corrected entry: Being an accomplished mystery writer and assuming that he had been injected with 100 mg of morphine, Harlan should have realised that his suicide would have been suspicious once they did the toxicology analysis.
LorgSkyegon
12th Jul 2020
Knives Out (2019)
Correction: If he died of an overdose then they would definitely do a toxicology report. He hoped that with an obvious alternative (suicide) they would not do one. Even with a lethal dose of morphine in his system, Marta would potentially be accused of malpractice, but she would not be directly responsible for his death and would (again, hopefully) be able to keep the inheritance.
He might have realised that once the family found out that he left everything to Marta, they would insist on an autopsy. Once they found the overdose, she would have been suspected of foul play.
Perhaps, but if he did not kill himself, it would be a certainty. He was trying to get the best outcome from a terrible scenario. Either way, it's not a plot hole.
Correction: Harlan was doing the best he could on extremely short notice.
LorgSkyegon