The motorcade passed the first assassin before he could do anything. The second...also fucked up and didn't do anything. The third threw a bomb at the cars, which bounced off the convertible top of the car, under the next car. The guy who threw the bomb at the motorcade then took a cyanide pill and jumped in the river. But he failed his suicide attempt. Only because the motorcade driver took a wrong turn did they succeed:

After learning that the first assassination attempt had been unsuccessful, Princip thought about a position to assassinate the Archduke on his return journey, and decided to move to a position in front of a nearby food shop (Schiller's delicatessen), near the Latin Bridge.[93] At this point, the first and second cars of the Archduke's motorcade suddenly turned right into a side street, leaving the Appel Quay.[89] When the Archduke's driver followed their route, Governor Potiorek, who was sharing the third vehicle with the Imperial couple, called out to the driver to stop as he was going the wrong way.[94] The driver applied the brakes, and when he attempted to put the car into reverse gear he accidentally stalled the engine close to where Princip was standing.[95] The assassin stepped up to the footboard of the car, and shot Franz Ferdinand and Sophie at point‐blank range[94] using a Belgian-made Fabrique Nationale model 1910 .380 caliber pistol.[96]

https://en.wikipedia.org/wiki/Assassination_of_Archduke_Franz_Ferdinand