would be very difficult to identify him. I used to cross this bridge on daily basis last year and this practice of throwing coconuts, flowers, coins (don't know why) is regular one.
even in bus you'll find people doing so, and in train there are numerous people attempting this.
problem is, as soon as they throw, they close their eyes to recite some prayer, so i'm highly doubtful the person who did this is even aware of what he/she did.