2009 Remake
Garber was involved the whole time.
Expanding on Alternative Character Interpretation, in the 2009 remake it is never established beyond a reasonable doubt that Garber wasn't involved. The entire movie could have been a Xanatos Gambit by Garber, as evidenced by him arriving home happy at the end - not mentally exhausted or breaking down from the stress. He could well have been The Man Behind the Curtain, Hiding in Plain Sight - Ryder and the others taking the car may have had no idea Garber was a part of this. He had to resort to some Xanatos Speed Chess, and then taken advantage of the chance to remove loose ends for himself or a larger organization he was working for. After all, someone had to be watching the stocks and selling before the price went too far back down. Of course Garber didn't care about stealing any of the $10 million cash - it's established that the 10 million is chump change next to the amount that was made on the market. In the end, not only did he make a large amount of money for himself and/or the organization he is working for, but he's also being hailed as a hero by the mayor and will be able to dodge the bribery charges against him.1974 Original
The Japanese officials were trolling Garber
During their introduction, none of them tell Lt. Garber that they speak English during the tour. They decide to keep that little tidbit to themselves just to mess with him and make the tour a bit less boring. When they deliver their coup de grâce at the end they reveal that yes, they understood every word that Garber has said, and they did it to just to see the look on his face. No one ever said that the Japanese didn't have a sense of humor.