How does a car-bomb anywhere in the world get by checkpoints? I would even think it could pass by the Turkish checkpoint on the border. How exactly can you check? Maybe you'll want to check if the passengers are acting suspiciously, but that is only a big if.
Are there any scanners or something that can see if there is a bomb in a car? And if so, does FSA have this type of equipment?
Assad was in control since 2000, and he may have done a good job. But when this problem started he was in control as well, and that makes him responsible. That's what leadership is, they are responsible for all the good as well as bad things that happens to their respected country's.
The best thing for Syria would be Assad stepping down and install a temporary government. If Assad gets brought down by force, then there is a big chance that various rebel groups might fight each other and/or the newly established government, because they all have a different vision when it comes to the future politics of Syria.
Assad staying will be problematic, because I doubt the fighting will stop if he stays, unless he is able to wipe out all of the opposition. The sole reason of the fighting is because Assad is in power, so the problem lies with Assad.
An election under the current Assad government would be hard to do, because the Assad government can't provide enough security in the country to go for a general election. There is fighting going on all over the country, and various parts of the country are under the rule of the opposition. The UN wouldn't and couldn't take the risk.
Also about the car-bomb on the border. The people responsible got caught and are being interrogated. That's pretty solid proof on who are behind this event. You can claim it's a conspiracy from the AKP government, but why would I believe that? It's nothing but speculation and conspiracy. Assad is also struggling and it is important for them to sway public opinion to their side, so to be honest, I expect any type of mis-information coming from their side (as well as FSA for that matter).