I’m dubious the ABC info is breaking because CNN has had the same info in a much more clearly worded form for a while now....
This is the same info as presented by CNN:
“At the time of the later shootings at Norris Hall, police were investigating a “person of interest” in the dormitory shootings, Flinchum said. But the man — a non-student who knew one of the victims — had not been arrested, and it is unclear if he has any link to the other gunman, he said.”
The way CNN words it it makes it sound more like an early mistake (which explains the lack of a response on campus, etc.) rather than a genuine second suspect.
If I am not mistaken, the police admitted they may have been chasing the wrong suspect at one point. But they never elaborate, and there were no follow-up questions.