Police still don’t know who killed Mackenzie Cowell.It’s been three months since 17-year-old Wenatchee teen Mackenzie Cowell mysteriously turned up dead. In that time, police have tracked more than 750 tips, interviewed hundreds and taken DNA samples from dozens of potential suspects.Despite the full court press from investigators, and the normal amount of media attention focused on the death of a popular and pretty high schooler, police don’t seem to have any substantial leads. Which is why Mackenzie’s mom Wendy is speaking out.”I know that you out there know who did this, and it’s important for my family and I for you to bring that person forward,” Cowell told KIRO 7. “You owe it to Mackenzie’s honor, and to us and to this community that she affected in such a positive way.”For more on Cowell’s disappearance and death, click here. For an unembeddable video of Wendy’s interview, try here.