Nearly 6,000 Boston Marathon entrants were still on the course when a pair of bombs detonated at 2:50 PM, according to a Yahoo News analysis of the time splits for each of the 23,200 contestants.
Of those stilling running, 1,400 were within two kilometers of finishing the 42-kilometer (26-mile) course when the detonations occurred. All told, 4,450 people made it to the 40-kilometer mark but did not officially complete the last two kilometers, mostly due to the blast. The popular marathon was staggered into three waves, so some entrants did not begin until 10:20 a.m. or 10:40 a.m.
The following interactive map of the Boston Marathon route visualizes how many runners were at each kilometer marker over the course of the race. Click "Play" to animate the graphic or use the arrow buttons to advance it manually.
Entrants post 10 time "splits," or measures of progress, along the race: One every five kilometers, plus the halfway point and the finish line. For visual continuity, this graphic estimates each runner's progress between splits by assuming a constant velocity. The graphic goes through 4 p.m. because those farther back in the race continued to run for some time.