White smoke? sounds like a sudden decompression not necessarily smoke from an explosive charge. now if you wanted that aircraft out of the sky, but wanted to give the pax some chance of survival (and leave as little evidence as possible) maybe you would consider a dummy round? radar guided so as to impact the structure not the engines which would probably lead to an explosion. with a hole in it things are going to start dropping off before the main crash site.
pure speculation but for me it seems to fit the limited evidence we have since as has been mentioned we do appear to have a news blackout. read one report that at least one body was found at secondary crash site.
overpowering hijackers is a good story and has been allowed to run without proper media scrutiny.