Here's a little Flavor text research:

Night descends on the town, and people start getting busy.

“Now’s our chance to start to even things out don’t you think?”

“Of course…..divide and conquer after all, with just enough confusion, perhaps we will be getting some help with that.”

“So, now prove your loyalty, go to that stuffy professor, he doesn’t seem to be sitting with the rest.”
In the show Pestilence says that the sole purpose of disease is to "divide and conquer". Since Lucifer was the one controlling the Horsemen he needed them to "prove their loyalty". So the first person talking is probably Lucifer, and the second Pestilence. Pestilence DOES have telekinesis, so maybe he's the one that killed Brett and not a Demon; see: http://supernatural.wikia.com/wiki/Pestilence

Imma do some more digging.