Firefighters battle the blaze in Manhattan's fashionable East Village where the explosion happened, March 26. [Photo/Xinhua]

NEW YORK - Authorities shifted their focus to what caused the Manhattan apartment building collapse and the possibility that someone may have improperly tapped a gas line serving one of the buildings, after two bodies were pulled from the rubble.

The names of the two men found Sunday were not immediately released. Authorities believe they are the two men reported missing after Thursday's explosion and fire that leveled three buildings and injured 22 people, including four critically. They were identified as Moises Lucon, 26, who worked inside a ground floor sushi restaurant, and Nicholas Figueroa, 23, a bowling alley worker who had been there on a date.

A spokesman for the Figueroa family confirmed to reporters at the city Medical Examiner's office on Sunday that Figueroa's body was pulled from the wreckage.

"There's reason to believe so far that there may have been inappropriate tampering with the gas lines within the building, but until we get full evidence we can't conclude that," Mayor Bill de Blasio said Sunday.

Fire Commissioner Daniel Nigro said crews should reach the cellar level where the explosion took place by Monday.

"When we reach the level of the gas piping, the way the debris is removed will change so that those who will investigate the mechanics of what happened will have access to that without it being torn apart," Nigro said.

In August, utility workers had discovered that the gas line to the restaurant had been illegally tapped, according to Consolidated Edison. The discovery led Con Edison to shut down gas service to the building for about 10 days while the building owner made repairs. Gas service was restored after the utility deemed it safe, the utility said.

Inspectors from the gas and electric utility Con Ed visited that building about an hour before Thursday's explosion and determined work to upgrade gas service didn't pass inspection, locking the line to ensure it wouldn't be used and then leaving, officials said. The work underway was to put in a bigger line to serve the entire building, Con Ed President Craig Ivey said.

Fifteen minutes later, the sushi restaurant's owner smelled gas and called the landlord, who called the general contractor, Chief of Detectives Robert Boyce said. No one called police or Con Ed.

"The focus of the investigation is not on infrastructure ... it's focusing on the work that was being done in the basement of those locations, that's what we're focusing right now," said Joseph Esposito, commissioner of the city's Office of Emergency Management.