National Transportation Safety Board: The official federal probe of the collapse is now scheduled to be complete in 90 to 100 days. In January, NTSB Chair Mark Rosenker said that under-designed gusset plates put in place when the bridge was built in the 1960s -- not shortcomings in bridge inspections in the years since -- likely played a key role in the disaster. This week, Rosenker revised his position, saying the agency was still studying whether signs of stress in the gusset plates years before the collapse might have been missed.
Wiss, Janney, Elstner Associates: Gov. Tim Pawlenty and the Minnesota Department of Transportation gave the Chicago-based company a $2 million contract soon after the collapse to conduct a separate investigation, and also to serve as an expert witness for the state in any legal cases arising from the collapse. Though Wiss Janney was hired to do a "parallel" investigation, the company has in more recent months worked in tandem with the NTSB. Wiss Janney project manager Michael Koob said the report is nearly finished but won't be released until after the NTSB rules.
Gray Plant Mooty: The Minneapolis law firm was hired by the DFL-controlled Legislature to investigate issues surrounding the collapse, but it did not concentrate on finding out why the bridge fell down. In May, the law firm issued a report that said state transportation officials had struggled for years with a lack of money for repairs, had a confusing chain of command and missed opportunities to detect potentially serious problems with the bridge.
Minnesota Legislative Auditor: Focusing on the state's overall transportation system, Legislative Auditor Jim Noble said in February that the condition of the state's highways was declining, and that without new money the state could do little more than maintain current roads.