It is quite common to know something about the recent behavior of someone that has some connection to a crime but not know who they are.
You might not know who robbed the bank, say, but you know their getaway car was a red Corvette with a license number that ended in 6. Or you might know that a recently killed body was disemboweled with a Kobalt brand model #TRS-5CF-K34714 trenching spade (it was left at the scene) and your forensics people were able to determine that it had not been used before this so was probably recently purchased.
In the first case, you are going to ask your state's motor vehicle department for a list of all registered red Corvettes in the area of the robbery. In the second case you are going to see if any Lowe's in the area (Kobalt is their house brand) can tell you who recently bought a #TRS-5CF-K34714 trenching spade.
You aren't asking because owning a red corvette is incriminating, or because owning a #TRS-5CF-K34714 trenching spade is incriminating [1]. You are asking because whoever did the crime is probably either in the set of red corvette owners for the robbery or the set of #TRS-5CF-K34714 trenching spade owners for the disemboweling, or someone in those sets is connected to whoever did the crime. Even if the connection is innocent talking to them can be useful--the red Corvette may have been a ride share, for example, and the driver had no idea he was serving as getaway driver, but he still may be able to provide details about the robber that will help find him.
Here it sounds like they determined that there was someone connected to the shooter and they wanted to find that person but did not know their identity, but did find out somehow that it was likely they had read that article within a 35 minute window on a particular day (I have no idea how they would have found that out).
[1] I own one. It's great!