Mayor Bill de Blasio Thursday throttled back a push by NYPD Commissioner William Bratton to get more Tasers after police shot and killed an emotionally disturbed Long Island man who stabbed an Hasidic student inside a Crown Heights synagogue.

An officer fired one fatal gunshot at Calvin Peters of Valley Stream during a stand off inside the world headquarters of Chabad-Lubavitch. A previously unpublicized surveillance video viewed by Newsday showed Peters was shot as he moved toward two officers who appeared to be boxed in by bookshelves in the synagogue library.

"This isn't something we've locked down," de Blasio told reporters about the Taser issue during an appearance in the Bronx Thursday.

On Wednesday, Bratton said he wanted to acquire 450 additional Tasers for the department stockpile. The NYPD has more than 600 Taser devices in use in patrol precincts, Housing police and transit units, as well as in central booking facilities, said NYPD spokesman Brendan Ryan.

When an officer gunned down Peters early Tuesday after he had stabbed the student, critics questioned why Tasers weren't used initially.

Bratton said that only patrol sergeants are authorized to carry the device.

Levi Rosenblat, the wounded student, remained in the hospital Thursday, but his condition was improving, said Assemblyman Dov Hikind (D-Brooklyn).

In the Bronx, de Blasio said he still supports adding more Tasers, but the cost and training required to use the devices need to be considered.

"The commissioner, I think, has it exactly right," de Blasio said. "So we've got to do more work to determine exactly how much we want to use Tasers, what we think the protocol and training should be, and then there are the financial issues, too."

Budget issues for the Tasers will be worked on during the budget process in January and February, the mayor said.

Officers assigned to the Staten Island Ferry started a pilot training program on Taser use in July, Ryan said. So far this year officers have used Tasers more than 300 times, compared to 200 times in 2013, officials said.

The synagogue attack has sparked debate in the Jewish community about what security measures should be in place, Hikind said. But another question centered on why Peters chose to travel from Long Island to Brooklyn to stage his attack, the assemblyman said.

"Why did he pick this location? There is absolutely nothing at this moment that gives us any indication," Hikind said.