By January 1, hundreds of people being held in city jails awaiting trials are expected to be released.

That's when a new state law takes effect eliminating cash bail for most misdemeanors and nonviolent crimes.

"Come January 1st, we’re a resilient organization, we’ll adapt, but I have real concerns,” said Police Commissioner James O'Neill.

Criminal justice reform advocates say 40 percent of the inmates in city jails when the law was passed this year would not have been incarcerated had the law been in effect when they were arrested.

"So the fact that the legislature wanted to really move away from mass incarceration, wanted to really make sure we were not holding people in jails because of small amounts of money, that’s absolutely right,” said Mayor de Blasio.

The case of Kalief Browder was a catalyst for the change. He was 16 years old when he was charged with stealing a backpack that allegedly contained a camera and money.

Unable to pay his bail, he spent three years in jail, two of them in solitary confinement. He eventually killed himself after being released.  Although he supports bail reform, Mayor de Blasio says he has some concerns.

"I’m not a fan of forgetting to give judges the ability to make a judgment based on the dangerousness of the suspect," said de Blasio.

NYPD officials including incoming police commissioner Dermot Shea are concerned because under the new law, even defendants accused of minor offenses who have committed violent acts in the past must be set free until their trials. Shea says he supports bail reform, but doesn't want such defendants automatically released.

"Of course, because ultimately we have the responsibility of 8.6 million people to keep safe and anything that could disturb that delicate balance that we keep," said Shea.

The city is working on ways to make sure defendants will show up for court dates after being released.

The Manhattan district attorney has pledged $100 million and the city council $7 million for pre-trial supervision.

Judges can refer defendants who can't be held on bail to these programs for support services and resources.

And in an effort to entice people to show up for court dates the city will give them things like Met's tickets and gift cards.

“If small incentives are part of what actually makes it work than that’s a smart policy," said de Blasio.