A man sitting on the concrete wall has a line-of-sight into JonBenet's bedroom and balcony because it is higher in elevation than either of the other vantage points.
19 cigarette butts were found by a neighbor's shed as reported in the case files; the likely place to do that is in the alley, on top of, or around, the Colby's concrete wall.
This collage from available Survey Plats on deposit at Boulder County. It depicts an imaginary line-of-sight from the concrete wall at the northeast corner of the Colby's property, across the alley, into the backyard to JonBenet's Balcony.
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jonbenetramsey.comRemembering JonBenét - The Unsolved Murder of JonBenét Ramsey
Remembering JonBenét - The Unsolved Murder of JonBenét Ramsey