Serial: Who killed Hae Min Lee?

Hae Min Lee was a high school senior in Baltimore, Maryland, who disappeared on January 13, 1999. When her body was found a month later on February 9, an investigation ensued that relied heavily on information provided by Jay Wilds, a marijuana dealer who had graduated from Hae's high school. The police claimed to have focused on Hae's ex-boyfriend, Adnan Syed, following a tip from an anonymous caller and information provided by Jenn (a friend of Jay but not of Adnan). After Adnan’s conviction, the case was featured in the podcasts Serial and Undisclosed, and some of the new evidence and arguments led the court to overturn Adnan's conviction and grant him a new trial. Followers of the case have made maps containing significant locations, multiple possible timelines have been suggested, and debates have ensued on forums such as Reddit.

At trial, the prosecution claimed that Adnan killed Hae and then called Jay for help only twenty minutes after school ended, at 2:36 PM. After a few side trips, they allegedly buried Hae’s body less than six hours later, around 7:00 PM. While the first trial could not come to a conclusion, after a second trial Adnan was convicted of first degree murder.

People who follow the case (as well as those on the jury) have wildly differing opinions on Adnan's guilt. This is expected in any case with many contradictory pieces of evidence, where none of them are clearly conclusive. When we try to analyze many, often contradictory, pieces of evidence with differing levels of reliability, human conclusions often prove incredibly inaccurate. This is exactly the kind of case where probabilistic inference can reach a far more accurate conclusion than a court or public debate.

Several alternative suspects have been suggested including Hae’s new boyfriend (Don), an unnamed drug dealer, as well as serial rapists or killers, most notably Roy Davis. Davis was convicted of raping and murdering another student from Woodlawn, but that case was still unsolved at the time of Hae’s murder, so Davis was not investigated regarding Hae’s murder.

Rootclaim's main finding is that Adnan is most likely not guilty (definitely not "beyond reasonable doubt" as required to put him behind bars), and that someone else is responsible. Of the specific suspects, Roy Davis is the most likely, although he still accounts for only 29%.

As always, this conclusion is based on a mathematical integration of many pieces of evidence and inputs, but can be simplistically explained as follows:

1. As a starting point, female victims are about 16% likely to be murdered by an ex-boyfriend, and 12% by a stranger (of whom Davis is just one of millions).

2. Jay's eyewitness testimony corroborated by Jenn dramatically increases the likelihood of Adnan’s guilt. While such testimonies do occur when the suspect is innocent (false informant testimony in 17% of DNA exonerations), they are, of course, much more likely when the suspect is indeed guilty. However, the many contradictions and the way the testimonies of Jay and Jenn correlate with the police's misconceptions (along with the rest of the evidence) imply that these testimonies were a result of police pressure. Together with the lack of any physical evidence against Adnan, and the pieces of evidence that support the other hypotheses, the effect of the testimony mostly cancels out. This leaves the likelihood of the hypotheses that Adnan is the killer at approximately 15%, which is about the standard likelihood of an ex-boyfriend with no testimony given against him to be the murderer.

3. The analysis of Roy Davis is very interesting, involving several calculations. While he is initially just one of millions, rare coincidences need to be explained if he's not involved. Namely: he lives along the victim’s planned route when she disappeared, and he previously murdered an 18 year old girl in a similar pattern (daytime abduction, strangulation, and leaving the body in a park). By carefully assessing the probability of each such coincidence, the Bayesian calculation can estimate whether together they are strong enough to overcome that very low “starting point”. The main factors taken into account are:

   1. Davis is 1 of 60,000 strangers in Hae’s vicinity (based on demographics of Hae’s neighborhood).

   2. Being a past murderer implies that Davis is 600 times more likely to be Hae’s killer (based on local crime statistics).

   3. Living on the victims planned route - 6 times more likely (based on how much of the population of Woodlawn lived on Hae’s usual route).

   4. Similar previous murder pattern - 24 times more likely (based on the similarities and differences between the murder of Hae and Davis’ past victim).

   Overall the combined effect of all the coincidences is 86,000:1, which is higher than the initial 1:60,000, making Davis a very likely suspect among “strangers”. While strangers initially account for only 12%, the lack of evidence against any other specific suspect increases this likelihood dramatically, reaching a final conclusion of 29% that Davis is the killer.

4. The option that Don, Hae’s new boyfriend, was the killer was found to be highly unlikely. While there is place to doubt the validity of Don’s alibi, the evidence that suggests that Don’s alibi was false is not strong enough to incriminate him. Additionally, Don and Hae’s relationship was new, and there was no reported friction between them - both unlikely if Don was the murderer.

5. It is worth considering whether Jay himself was the murderer, but with no evidence other than his testimony, this is not enough to overcome the weak relationship that he had with with Hae and the apparent lack of motive.

6. The prosecutor’s case, that Adnan killed Hae around 2:30 PM and buried her at 7:00 PM, is easy to exclude even without a probabilistic analysis - a medical examination of her body shows that after death she was left in the same position for at least 6-8 hours without being moved. Amazingly, this is the version that the jury used to convict Adnan “beyond a reasonable doubt.”

7. Since it is unlikely to have been Jay, Don, or Adnan, and only moderately likely that Roy Davis was the murderer, the most likely conclusion is that it was someone else.