Burner phones don't work like they do on tv. Any law enforcement can track a burner phone and trace it to you with in a few hours.
You buy a burner phone from x company with cash.
You insert sim and connect to a tower. Your phone then follows you around moving from tower to tower.
The police put up a cheap and easy to use spoof tower. Every cellphone in the area will now connect to the that tower, the police set it to forward to a normal tower. Open source software like openbts is used. It does not collect any information that is encrypted, so completely legal with out a warrent But it collects the open sim number from your burner phone.
In this case. They put a tower next to laundries home collect the numbers. Wait until the leave the area, follow them and collect the numbers. The numbers that follows them around is their burner phone. Then you get a search warrant for that sim.
Even in large crowds, they simply spoof the tower, take pictures of the group, then follow the people around isolating one sim at a time. Using photo id software to get names.
This has been a problem for a long time and the FBI has been using it for a long time. Random search
The FBI Uses Fake Cell Towers to Do Real Spying