Many hands make light work and any info I provide will be argued against.
However here is what I firmly believe to have caused it, seeing the protests in the country that have been instigated via media and online means, CIA operatives that are in fact foreign mercenaries paid by the CIA/US took advantage of the situation.
They infiltrated Syria and positioned themselves in an elevated place with sniper rifles then fired into the crowds of protesters and the police/security forces, coming under fire the police and security forces returned fire.
At first there was only a handful of foreign operatives which made it much easier to hide their presence, however inside the borders of Turkey and other neighboring states hundreds more American / Saudi and others of their allies, had funded and equiped fighters were waiting.
These fighters then moved into heavily populated areas and used the buildings and civilians as human shields, being armed with M16 and other US weapons that are far more useful as sniper rifles, they have been able to inflict casualties from a distance.
Yes the Syrian army has used their tanks and mortars etc, however I cannot see that they have any other choice, these are extremist fighters from all over the world, they are using all the tactics you would expect from extremists, car bombs, public executions of men women and children.
What the TV is reporting is just lies, yes the Syrian army will have killed civilians in the cross fire, however a lot of the reports and footage that is coming out of Syria of atrocities commited by the government is in fact being commited by the FSA.
Do you not think that in the interests of fairness and justice, you should be interested in finding out what is actually happening?