Your proposition:

1. Cities increase police funding in response to increased crime

2. Therefore, decreasing police funding increases crime.

However, 2. does not follow from 1, since many other factors affect crime rates, from legislation to enforcement and from social issues to societal issues.

In fact, even the inverse of 2. does not follow from 1: increasing police funding does not decrease crime rates.

If you disagree, please provide an academic source for the direct causal relationship between police funding and crime rate.