At a law enforcement press conference in Boston Tuesday, Richard DesLauriers, special agent in charge of the FBI’s Boston office, said the investigation will be a worldwide one. Noting that this “very complicated investigation” is still in the early stages, he vowed that it would be pursued methodically, diligently and with a sense of urgency.

Investigators recovered a circuit board that is believed to have been used to detonate the two explosive devices which were made in pressure cookers or “relatively ordinary cooking devices.” Heavy nylon bags with nails and ball bearings have also been recovered from the crime scene. Massachusetts Governor Deval Patrick wanted to clarify there were only two explosive devices. Debris found on rooftops and embedded in area buildings, which indicates the scope of the blast, is also being examined.

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The National Guard, which is helping with random bag checks among other things, will remain in Boston as long as they are needed. DesLauriers said investigators have received a tremendous outpouring of video footage from the public and he asked any additional area businesses to come forward with any video they might have. In addition, specialists from Quantico (a U.S. Marine Corps base) have been called in to help with digital analysis of the video.