Possibility of Criminal Charges in New York City Building Collapse Growing

— -- As searchers and cadaver dogs sift through the rubble looking for victims and evidence, New York City officials tell ABC News that the possibility is growing that criminal charges could be filed as a result of the blast and building collapse in the East Village.

Investigators with the Manhattan District Attorney's Office are now fully engaged, according to a law-enforcement source, as opposed to simply "monitoring" the investigation -- which would be the standard procedure.

"They are on-site and they've given instructions" about what type of information may or may not be released by other city agencies, the source said.

The Manhattan District Attorney's Office is not commenting at this point.

Two city officials tell ABC News investigators are now pursuing reports from tenants that they were told by building management to report gas problems to the landlord and not the energy company, Con Edison, or to 911.

Some tenants have told investigators that they were given those instructions as late as Thursday morning -- just before Con Ed inspectors were scheduled to examine plumbing in the basement.

Investigators have not yet confirmed these reports. But if they are found to be accurate, it could prove to be critical. Investigators and prosecutors are trying to determine whether the piping work done in the basement was legal and done appropriately, or if the building's owners knew they were violating the city code and, thus, might be jeopardizing the safety of people in and around the building.

Specific instructions to tenants that they should not call the city or the utility could be a key indicator that someone knew the gas piping might not be up to code, the officials said.

It is these reports, the officials said, that prompted Mayor Bill de Blasio to be so emphatic in the last couple of days as he reminded people during his briefings that gas odors must be reported immediately to the city or the utility. He stressed that no one should rely on simply calling their landlord.

The owner of the ground-floor restaurant where the explosion occurred called the landlord to report the gas leak Thursday, and it is that leak that is believed to be the cause of the blast.

Though the mayor has cautioned that the cleanup and probe will take time, investigators want to get into the basement as soon as they can to examine the gas pipes. They believe those pipes will provide the most crucial evidence.

Two people were still missing tonight, and 22 people were injured in the explosion and collapse.