How does James Garfield's assasination relate to civil service reform?

At the time of Garfield's assassination, the spoils system was still very much in operation. This meant that civil service jobs would often be given to friends and associates of the President as a reward for their loyal service. Inevitably, the system was open to widespread abuse and led to rampant corruption. The federal government became crammed with political hacks and cronies, whose sole qualification for office was that they happened to support the current President. Many of these political appointees took advantage of their positions in government to line their own pockets at the taxpayer's expense.
One man who hoped to hop aboard the Washington gravy-train was a certain Charles Guiteau. A deeply disturbed individual, he'd got it into his head that he'd helped Garfield win the Presidency and was due a reward by way of a plumb government job. When such employment didn't materialize, and convinced that Garfield was going to scrap the spoils system, Guiteau shot the President dead.
This tragic incident convinced many that the time had come to scarp the spoils system once and for all. Civil service reform soon came in the shape of the Pendleton Act of 1883, signed into law by Garfield's successor, Chester A. Arthur. Though quite a modest measure on the whole, the new Act introduced a greater degree of professionalization into the civil service by providing for the selection of some positions by way of competitive examination rather than through political patronage.