You may be right about that resting mainly on Jennifer Niswender's say so.
Here's the detail I've been able to find quickly, searching in the early threads:
Jennifer said police have told the family there were no signs that a "sexual assault or struggle" took place.
"That's what they said right from the beginning," Jennifer said... .
[Ypsilanti police Chief] Walker declined to provide additional details about the case, including whether Julia may have known the individual responsible for her death.
"I can't get into any of that," Walker said. "These detectives have a difficult case and have been working vigorously. It's not a clear-cut case.There's some sensitive information. ...The fact that the family is going public, I can't control it."
From the Ann Arbor News, K.Stafford, Tue, Apr 9, 2013 : 9:30 p.m.:
http://www.annarbor.com/news/ypsila...-confirms-julia-niswender-drowned-in-bathtub/
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Per verified family member Trojan1966:
As far as I know or have read, there was no signs of sex but nothing to say that it may have been the reason and someone went way too far. The strangulation caused her to go unconscious after which she was put in the tub. Whoever did this, must have been very good at it as the Julia I knew would have put up a heck of a fight. Evidently there were no signs of a struggle which really surprised me when I heard that.
The above from this post of Trojan's:
http://www.websleuths.com/forums/sh...-Ypsilanti-Dec-2012-2&p=11629898#post11629898
I'll see if I can find more. I think there's also some MSM reporting on the absence of physical, signs of trauma. Not quite the same thing, I'll grant, but part of the picture.