In picture 3017_067743, a "shadowy" figure shows appears underneath a stoplight at the corner of Santa Monica Blvd and Doheny Dr, the intersection right before the 25K timing mats. In photo 3017_067776 you can see the shadowy figure is wearing a baggy blue shirt, dark (black) long sleeve shirt, long dark (black) shorts, and dark (black) running shoes. On page 4237 the shadowy figure has hands on hip, waiting for an opportune time to jump back into the course. This is the perfect intersection for a "pedestrian" to cross the street without much attention and all of sudden turn into a "runner" halfway across. Frank is using his bib belt to possibly obscure his number but it's not uncommon to see many walking marathoners in the LA Marathon - just too early to be doing so in a 2:50 pace group..
By page 4238, Frank is clearly on the course and the "shadowy" figure below the stoplight is gone. Frank just happens to be wearing a baggy blue shirt, a black long sleeve tech shirt, long black shorts, and black running shoes! His attire matches the shadowing figure below the stoplight piece for piece. Runners 40874 and 1008 pull away from Frank within a few strides on page 4238.
https://www.finisherpix.com/gallery/singlephoto/en/usd/3017/3017_067743
https://www.finisherpix.com/gallery/photobrowser/en/USD/3017#All/Run/4234
https://www.finisherpix.com/gallery/singlephoto/en/usd/3017/3017_067776
https://www.finisherpix.com/gallery/photobrowser/en/USD/3017#All/Run/4237
https://www.finisherpix.com/gallery/photo/en/usd/3017/1151/3017_246511#3017_246511
https://www.google.com/maps/@34.0796287,-118.3897198,3a,90y,319.1h,88.09t/data=!3m6!1e1!3m4!1s2nQAcaiqb88wUqVp0Z4lbg!2e0!7i16384!8i8192