Countering a flurry of reports that suggested there were multiple unexploded devices scattered throughout Boston, NBC’s Pete Williams reported Tuesday morning on MSNBC that a senior law enforcement official said the only explosive devices in the city were the two that erupted near the finish line of the Boston Marathon.

Williams said a number of bystanders dropped what they were carrying and ran after the deadly explosions, leaving scores of unattended packages throughout the city. Several of those packages were detonated by authorities, according to Williams, but there is no indication that they were unexploded devices.

Williams noted that it is somewhat disappointing for investigators that there were no unexploded devices, which might have represented an “investigative gold mine.”

Becoming more plausible that this could have been the work of just one person. Breivik’s assumption, and it seems fairly reasonable, was that someone not on a watch list had a 30% chance of being apprehended before a bombing plot was completed, but that the risk rose to 90 to 95% by the time 5 people were involved.