this is NOT a fact...just a theory....
when DD met with the guy who killed vrinda kids...the killer looked exactly like Sameer in the dark and koki was surprised/happy to see him....and remember when Koki wanted a way to get a hold on Vrinda so she can rule and his father said that he knows the guy who killed vrinda kids and they would benefit from this situation....its pretty clear, once vrinda learns that sameer killed her kids she would be devasted b/c she considers janki as her daughter so obviously sameer means a lot to her and so janki/vrinda would be heartbroken and this would cause a drift between them and koki would get a chance to taunt vrinda and she would leave eventually, making koki the ruler again...its pretty obvious that DD knew the killer b4 hand otherwise he wouldnt make him run from the scene...and sameer being innocent/scardy cat listened to DD and escaped[ this accident probably happened b4 sameer marriage to Janki, every1 knows how sameer was b4 his marriage so it makes perfect sense]...i am sure this is the huge twist coming up....mahesh cant be the killer b/c it would upset koki and DD and they would loose from this situation....so it has to be sameer or some1 close to vrinda that Gheewalas also know too....share ur views...
*my bet is still on sameer....but i wish it was sum1 else or sum1 new since sameer-janki relationship has faced enough problems already so they deserve a break.