Okay, you may not agree but I'm going to say it before my head explodes anyway...and then you can kick me.
Let's say the roadblock WAS related to this case since it's pretty transparent. They set this roadblock up between Bryant and Coleman Rd, right? The only possible way LE could ever hope to find THAT particular gun on someone in THAT specific location...is if he LIVES between those two roads. They haven't got probable cause to search his residence, they believe that he has the gun but have no concrete proof because it's not registered....so they set up the roadblock hoping to catch him coming away from his residence with the gun on him. They are free to set up roadblocks wherever they wish. Then all he has to do is go through there, act suspicious, and they have an excuse to search the vehicle. Picture it. Let's say LE purposely sets up this roadblock 123, on the sly, while this guy is at home. If he leaves home with that gun, he has no idea there's half a roadblock waiting for him whichever way he goes. They were hoping he'd panic, freak and act oddly.
Just a theory....but if this were true...then obviously it failed miserably. I'm just thinking that a Glock .40 cal is a gun you get attached to if you're a gun freak. Glock makes an outstanding weapon. This one cost someone in upwards of $600, minimum, if he bought it new. It's designed for one thing..what this one was used for in this instance. LE is probably of the mindset that either the person who has it doesn't know it was used for this purpose or doesn't want to come forward and say that he thinks that it was. And I bet they're thinking that if you've got a Glock .40....you keep it. I have a .9mm (model 19) and I wouldn't trade it for nuthin'.
They sent letters out looking for Glock .40's. Then they set up a road block right around the crime scene. They know that gun is down there somewhere...CLOSE. They announced that they were looking for that gun and someone squealed. They just aren't sure yet if the information is credible. They're trying to flush him out.
I think the gun testing was done strictly in the hopes that, if teens had borrowed Daddy's gun without him knowing about it, committed the murders and then quietly put the gun back where it was kept, they'd find the killer/killers.
Sigh. I'm thinking the gun testing and the roadblock are both just shots in the dark. (The latter just an attempt to find some other witness.) As Jessica Brown has let us know, they have nothing right now.