Rest in Peace Katie and dear friend Bowie, and heartfelt condolences to all who loved them.
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I believe we now know that the jogger has spoken with police.
The newer image of the guy in the white shirt is the third image that has been released. Timestamps are 12:25:05, 12:25:07, and 12:25:10 AM. Stride is distinctly much longer in the latest image released at 12:25:10.
The red stain has been mentioned earlier.
I've enlarged the image of this individual, carrying a cane with what seems to be a distinctive white band near the mid to lower shaft of the cane. (Sorry, for some reason I am unable to upload the enlarged images, so members will have to enlarge it themselves.)
(top 2 images are reversed timewise)
I've enlarged, done colour inversion, and stared at that reddish brown blob for days now and really can't see it being anything other than blood. That is just MOO and I could be totally wrong.
Speculation here.
IF it is blood, surely there aren't many people walking out of the park, bleeding.
IF it is blood, it could be coming from an upper, under arm wound. I specify upper, under arm because there is nothing visible coming down the outer arm. I can visualize an under-arm wound coinciding with a dog coming straight up from underneath a raised arm. If an arm was raised in what may have been a blitz attack, with Bowie on a limiting, short lead (noted in the pic of Katie and Bowie in the crosswalk), it may have been difficult for Bowie to grab an extended hand/weapon, but coming straight up under a raised arm toward the armpit seems, IMO, very likely.
This person is only discussed as a potential witness, so hopefully he hears that LE would like to speak with him and will come forward so they can eliminate him as having any knowledge or involvement.