Officials: Some suspected mail bombs were not capable of exploding

In some cases, the flaws were substantial. In others, more subtle, they said.

The news, expected to be detailed at a joint NYPD/FBI briefing in New York shortly, comes after investigators said the devices appeared poorly made and that it was unclear if they were hoaxes or simply cases of bad construction. Earlier in the investigation, officials in multiple states had described the items as live explosives and a number of senior bomb techs briefed on the probe said they had all the components necessary for successful explosions.

Investigators cautioned that the analysis is far from complete, and they say anyone who encounters one of the parcels should treat it as dangerous.