The reason you would assume someone is missing is because responsible adults like Katrina would call into work or call and reschedule the job interview she had Tuesday, not just no show or "play hooky". So if work/interview called her home at Tetterhall and he answered or got the message that she did not show up that would raise alarms for people to assume she's missing at that point.
We don't know how the conversation went the night she went missing, it could have been left in the air that she would come back home or could possibly stay at the other place (be it condo loaned for separation, housesitting, whatever speculation you wish to believe). If she was just housesitting instead of living there for separation, perhaps it's possible some nights she went there and fell asleep there and didn't come home. If he's not involved maybe he fell asleep after she left and didn't wake up until the morning and realized she was gone, but could have been to the condo, or to the interview, or to work.
It's all good and well to be like WHY this WHY that, if it was me I would do this I would do that, but people forget that you are speaking from the current situation. You are not thinking of it from the perspective of prior to something bad happening. I mean when your loved one leaves for work or goes out the door to run an errand you are not assuming the absolute worst when they don't come back when they said the would. You never know when the last time you see or talk to someone could be the absolute last time you ever see or talk to that person, be it a car accident, a random shooting, or an abduction.
From the way it reads, it seems that LE found the car during their patrols, but I am not sure.
Well Roscoe police department is the closest to their home and if you search for Machesney Park Police Department you get Loves Park, Winnebago County, Rockford or Roscoe as being the nearest police departments to contact. So I guess for the area they live in, if they call 911 or they call the police it probably goes to Roscoe or Winnebago County.