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It wouldn't be necessary to clean her fingerprints off the window; children's fingerprints break down and disappear rather quickly. Crime shows like CSI and it's many spin offs have led the public to believe that fingerprints are commonplace and easy to find and while that may be true in some instances, it's definitely not true with children's fingerprints.

The majority of what's left behind as a human fingerprint is water. These traces of water evaporate within only a few hours, causing the fingerprint to fade. The other major component of fingerprints are skin oils and fatty acids. In several studies, it's been found that children who have not started puberty have a much higher concentration of short-chain fatty acids which are much more volatile than their longer-chain adult counterparts. It's hypothesized that adult skin produces these oils mostly on the face and hair and that these oils are then transferred to the fingertips by the normal touching of these areas.

What this means is that children's fingerprints have a much shorter longevity than adult fingerprints. If you leave a child in a car for an hour, then leave the car in the sun on a hot summer day, you can literally watch as the fingerprints disappear from the windows, eliminating nearly all traces of the child ever being there. This greatly complicates police efforts to solve crimes involving children, especially kidnapping.

Sources:
http://www.osti.gov/bridge/servlets/purl/443195-5WENSh/webviewable/443195.pdf
http://infrared.als.lbl.gov/pubs/Sleuthing_with_Synchrotrons.htm