Rikers Island will be closed in 10 years.

Well, maybe.

New York City Mayor Bill de Blasio on Friday threw his support behind closing the notorious island of jails and moving all inmates off the island to other facilities throughout the five boroughs.

“New York City will close the Rikers Island jail facility. It will take many years, it will take many tough decisions along the way. But it will happen,” de Blasio said during the announcement in a City Hall rotunda press conference alongside City Council Speaker Melissa Mark-Viverito, who has pushed for the closure, and other city officials.

De Blasio said when he believes that Rikers could be closed when the average daily inmate population of New York City declines to 5,000 – down from its current 9,300, and less than one quarter of the city’s peak jail population of 22,000 in the mid-1990s.

“That’s the goal in this whole process,” he said. “We believe that can be achieved in the next 10 years. That is the goal that the speaker and I have agreed to. A 10-year timeline. Again, it will take a lot of work, and a lot of things have to go right.”

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“A lot of things” that have to go right include maintaining the historically low crime rates in the city and introducing bail reform policies that would keep more people out of jail as they await trial. Even more difficult, at least politically, would be finding sites to build new facilities in New York City that can hold a total of 2,600 inmates. Other existing facilities besides Rikers Island, including the Brooklyn Detention Complex in Boerum Hill and a barge off the shore of Hunts Point in the Bronx, hold a total of 2,400 inmates.

De Blasio said he would prefer fewer, larger new jails to replace Rikers, but even identifying locations to build two or three could be difficult. Many City Council members have publicly said they do not want jails in their districts since the conversation around closing Rikers began heating up more than a year ago, and Staten Island Borough President Borough President Jimmy Oddo, who has broad influence over new development on Staten Island,tweeted during the mayor’s announcement that de Blasio “must guarantee” that no jails will be built on Staten Island.

To those concerns, Mark-Viverito urged compassion. “These (inmates) are our neighbors, these are our family members. And we cannot forget that… We need to rise above that (negative) rhetoric,” she said.

Mark-Viverito, who championed closing Rikers in her 2016 State of the City, is term-limited out of office at the end of 2017. And even if de Blasio wins re-election  in November as expected, he would have fewer than five years left in office, leaving much if not all of the implementation of the plan up to a new administration.

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Mark-Viverito said that at this stage, the city is “laying the groundwork.” On the Slant podcast earlier this month, she pledged to remain an advocate for closing Rikers even after leaving office.

Many additional details for how the plan to close Rikers Island will proceed are expected on Sunday, when a independent commission on criminal justice reform created by Mark-Viverito and chaired by former Chief Justice of the state Court of Appeals Jonathan Lippman will release its report.

Until Friday, de Blasio had generally thrown cold water on plans to close the island, dismissing it as “noble concept” but too complicated to actually happen. Even while embracing the plan today, he seemed to urge caution.

“This will not be easy,” de Blasio said. “A decade is a long time. There will be a lot of tough choices.”

RIKERS PROPOSAL, BY THE NUMBERS:

9,300: current average daily inmate population across all New York City jails

7,000: rough number of those inmates in the 10 jails on Rikers Island

5,000: the inmate population that de Blasio wants to reach before closing Rikers Island

2,600: the number of new inmate beds that will be needed off Rikers Island

2027: the year when de Blasio hopes to have all inmates moved off Rikers Island