Continuity mistake: As the couple with their two children are walking down the street, the daughter, Sophie, is holding latex helium balloons which are the transparent type, but after she and her mother are struck by the reckless drunk driver, when the balloons float away they are the opaque type. (00:04:25)
Visible crew/equipment: When Erin walks into her office and finds Robert waiting for her, as she walks past him toward her desk, the green tape mark is visible on the floor near Robert's feet. (00:01:00)
Answer: It's a common cop show plot device. If the police on the show always acted in the most logical way (i.e. not alerting a suspect to their presence) the show wouldn't have the opportunity for an exciting foot chase.