In my opinion, LE knows and has proof of the suspect(s) involved. I believe they have received all of the digital forensics (phone, SM, camera) along with crime scene forensics (DNA, prints, etc) and interviews with family, surviving roommates, friends, old schoolmates, and fraternity/sorority brothers/sisters.
MOO LE is delaying the arrest of the suspected killer(s). I believe they have agents under surveillance waiting till after the holidays to make the arrests for the sake of the families (victims and LE).
IMO, LE is releasing tidbits to get information and input from the public on any additional accomplices or witnesses. This crime was a result of pent up rage from a person close to the victims and the killers left a messy crime scene that is making it easy to solve. Just wait till the New Year. IMO.