1985 1384
1986 1582
1987 1672
1988 1896
1989 1904
1990 2262
1991 2154
1992 1995
1993 1946
1994 1561
1995 1178
1996 983
1997 769
1998 633
1999 676
2000 708
2001 649 (not including the September 11 terrorist attacks).
2002 575
2003 597
2004 572
2005 530
2006 596
You can see a peak just before he became mayor in 1993, but not much of a drop (down 300 in 3 years). It then fell 900 in the next 3 years and 300 more in the next 3. It certainly does not look like a steady down trend before his terms.
So why are you surprised that Giuliani's strict laws brought down crime? NYC's excessive gun control legislation had been trying to wean them off of the 2nd Amendment for over eight decades.
If Giuliani had been mayor of some other city (one that didn't enact such heinous gun control policies), his crime-fighting measures wouldn't have been received so well. Just goes to show how far removed NYC is from conventional America in terms of political tilt; they're so far left that a fellow liberal like Giuliani is called a right-wing fascist because he has an (R) after his name.