From the report by the NY Civilian Complaint Review Board, pdf link. You make conduct rules for the cops, and the cops just keep doing what they do, with no accountability if they break policy (and none if doing so kills). The choke hold on the late Mr. Garner was the rule for use by NYC cops, not the exception. From the Report:

In July 2014, CCRB Board Chair Richard Emery, in the wake of the tragic death of Eric
Garner and on behalf of his fellow Board members, asked the CCRB staff to undertake
an objective, comprehensive assessment of chokehold complaints made to the CCRB.
This study investigates chokehold complaints, primarily from January 2009 until June
2014, in order to report findings and make recommendations to the Police
Commissioner and the public. After documenting and evaluating five and a half years of
chokehold complaints, their patterns and the likely causes of their persistence, this
report recommends ways in which the CCRB and the NYPD can collaborate to reduce
chokehold incidents and eliminate future chokehold tragedies. This report is an agency
report prepared by staff as directed by the Chair.....For more than 20 years, the NYPD Patrol Guide has prohibited the use of chokeholds, relying on a Police Department rule that unequivocally forbids any pressure to the neck, throat or windpipe that may inhibit breathing. This rule was plainly intended to prohibit all chokeholds. As defined, chokeholds, though not illegal, are unambiguously prohibited by Department policy.
This report reveals that officers have continued to perform chokeholds and, based on
the complaints the CCRB received from the public, the use of chokeholds appears to be
increasing despite the Patrol Guide prohibition. It also reveals that this crystal clear
prohibition has been degraded over the course of the last decade.
Put simply, during the last decade, the NYPD disciplinary decisions in NYPD
administrative trials of chokehold allegations failed to enforce the clear mandate of the
Patrol Guide chokehold rule.

CNN, in What's the Point of Police Body Cameras:

Despite the NYPD banning chokeholds in the 1990s, New York officer was accused of putting someone in a chokehold, on average, every other day from 2009 through the first half of 2014...