That is an excellent question and I suspect something that was done long ago. A formula of these show types is that they go over old discoveries and act like they just found it while working on this show. My impression is that is the cliffhanger that is going to get us to watch next season.

A huge problem is that the PD’s are still holding back information. The likeliest reason for this is the ever present liability.

We had a simple car burglary once where a victim stated to the officer that she thought she knew who broke into the cars because a problem tenant was the sort of person who would break in to cars. Worth putting in the report for detectives but not much to go on. Unfortunately one of the victims got a copy of the report and we failed to redact the "Suspect" info. Within hours our officers had to rush the complex because tenants were pretty much standing outside the suspect apartment with pitchforks. Now that was just for vehicle burglary. Imagine what would happen if they released data on a possible serial killer. Even if the suspect was dead they still have family. Agencies are scared to death about the liability of giving out too much info.

What really needs to happen and may already have for all we know, is that every investigator whether public or private, retired or the current steward of the Zodiac cases, needs to come together in a big room and go over every case step by step in chronological order. Get everyone who has any information in the same room sharing intel. Then establish a to do list and have a joint task force go handle the to do items. When I was a Detective I tried to bring every detective in the county together 4 times a year and when I succeeded the amount of cases we solved was amazing.