Emergency workers are searching for at least two people still missing after an apparent gas line explosion leveled three Manhattan apartment buildings while investigators piece together what exactly caused the blast that injured 22.

Special canine units sniffed for anyone possibly trapped beneath the heap of loose brick and rubble on Saturday, two days after the blast. Detectives issued posters seeking information on the whereabouts of two men believed to have been in the sushi restaurant on the ground-floor of one of the collapsed buildings: 26-year-old Moises Lucon, who worked at the restaurant, and 23-year-old Nicholas Figueroa, a bowling alley worker who had been there on a date.

Their families frantically searched, showing photos of their loved ones and asking for help.

"We have just been walking down the streets, one by one," brother Zacarias Lucon told the Daily News of New York. "We are just so exhausted and upset. I don't know what happened to him."

Lucon moved to New York about six years ago from Guatemala; Zacarias Lucon told his parents on Friday.

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Figueroa's family said they were holding out hope.

"My brother is strong," said brother Neal Figueroa told reporters. "Even if he is still in the rubble, I know he would still be in a predicament to get himself out and so I'm just praying for that."

Authorities also were exploring whether a third person was unaccounted for, Chief of Detectives Robert Boyce said. But as of Saturday, no one else was believed to be missing related to the explosion.

"There's a lot more we need to learn," Mayor Bill de Blasio said Friday, a day after the blast in Manhattan's East Village neighborhood.

It's possible that someone improperly tapped a gas line amid ongoing plumbing and gas work in one of the destroyed buildings, though investigators need to get into the basement to learn more, de Blasio said.

Inspectors from the utility company Consolidated Edison had visited the work site Thursday about an hour before the 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.

Fifteen minutes later, the sushi restaurant owner smelled gas and called the landlord who called the general contractor, Boyce said. Nobody called 911 or Con Ed.

The contractor, Dilber Kukic, and the owner's son went into the basement and opened a door, and then the explosion happened, burning their faces, Boyce said. Kukic, who is facing an unrelated bribery charge, declined through his lawyer to comment on the circumstances surrounding the explosion.

The building had an existing gas line intended to serve the sushi restaurant; the work underway was to put in a bigger line to serve the entire building, Con Ed President Craig Ivey said. As for whether the largely vacant apartments were getting gas from the existing line, "That's a great question," he said.

De Blasio wouldn't say more about why officials believe the existing gas line might have been tapped. But the building had a history: Con Ed found an unauthorized gas pipe there in August after getting a report of a gas smell, according to a city official briefed on the information. The official wasn't authorized to discuss the ongoing investigation publicly and spoke to The Associated Press on the condition of anonymity.

The pipe was gone when Con Ed checked again 10 days later, the official said. Some of the people involved with the building are not cooperating with investigators, the official said.

Dozens of neighbors have been displaced because of the blast, and a fourth building badly burned after the explosion remains at risk of collapsing, officials said.

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