About the Serial Killer. I think, if she accompanied Hawke to find the bones in Act 1 and fought the shades and demons with him, she knows there's magic at work.
We can tell Emerick this same information.
Now, Aveline isn't Guard Captain in act 1, but she did know about it, and she would've seen someone flee the scene right before we fight demons. And since we pass the report to Emerick who says he's taking it to his superiors, we can assume Meredith knows as well.
What we find is three years later that Aveline and Meredith both have dismissed the case and the evidence and Emerick forbidden from continuing his investigation.
In this regard, I'd say both Aveline and the Templars showed a huge case of incompetency.