Why and how was Caesar killed, and by whom?

Julius Caesar is killed in the Senate by the group of conspirators who had mutually decided that, for the good of Rome, they were obligated to get rid of him. According to the text, Casca is the first to stab Caesar, followed by the other conspirators, with Brutus being the last to join in. Caesar is horrified to see his "angel" Brutus joining in, saying, "Et tu, Brute?" He does not realize that Brutus, in fact, is the ideological leader of the conspiracy; although, he had to be persuaded to join it by his friend Cassius.
Immediately following the death of Caesar, Brutus remarks that "ambition's debt" has now been paid, meaning that the great ambitions of Caesar, which ran contrary to the good of Rome, have now been defeated. Having killed Caesar, the conspirators bathe their hands and arms in his blood as a symbol that peace and liberty have, by Caesar's death, been restored to Rome. The conspirators' fear had been that Caesar intended to become a king, something that ran contrary to the principles by which the Roman republic was governed at this time. Brutus is stating that in killing him, the action was not because he did not love Caesar, but because he loved Rome more.