concerned. david? >> rob marciano tonight. rob, thank you. we also have new reporting this evening after that gruesome discovery inside a family-owned business. four people discovered dead, and abc's alex perez is on the scene in north dakota with what we've learned. >> reporter: tonight, the murder mystery just outside bismarck, north dakota. police asking for the public's help, as they work to track down whomever murdered four people inside this management company building. the police chief here, like so many others, stunned. >> it's something that you'd never wake up in the morning thinking, this is the phone call i'm going to receive. >> reporter: police making the chilling discovery monday morning, after responding to a medical call at rjr, in mandan. the company manages apartment buildings. among the dead, police say, the owner and this married couple pictured on the company website. the murders rocking this tight-knit town. police say they believe the four were targeted, but revealing little else. >> it's a special kind of evil. that's all i can say. >> reporter: david, investigators have not revealed