So detail from the NPR interview this morning:
1) shooters cut comm lines before they begen shooting
2) shooters were firing “ak-47 type” rifles. presumably this mean they found 7.56 casings.
3)shooters fired 120 shots from 40-60 away from the transformers, at night, and managed to hit the transformers with 110 of them.
4)shooters had enough communications to be able to coordinate opening fire with the phone lines being cut, and to cease fire and disperse 70 seconds ahead of the police response.
They may not have know the details of the transformer, but they sure as hell seemed to understand how to run an operation.