i can't possibly believe that ATC controllers would not have said anything to them about sparks out of an engine. i also am wondering if there were warnings of any sort going off in the cockpit. i would imagine there were.
The controllers said they "saw sparks while the a/c was on take-off roll". They said nothing about sparks coming from the engines at all, you are only speculating on a accident that occurred less than 24 hours ago.
Take-off in any Learjet model takes only a few seconds, from the point take-off power is set to when the aircraft reaches a positive rate of climb. This leaves practically no time for a controller to see and then notify a crew of a problem, then expect that crew to be able to abort.
I know you're an ace 172 Jockey, but please remember the crews and the controllers are well trained professionals and would do anything within their power to prevent an accident like this.