A federal law enforcement official has identified the pilot in the Austin, Texas, plane crash as Joseph Stack and says investigators are looking at an anti-government message on the Web linked to him.
The Web site outlines problems with the IRS and says violence "is the only answer."
The IRS said in a statement that the small plane struck its Austin offices, where 190 of the agency's employees work. Officials say they are still trying to account for all the workers.
The official said authorities are looking for a motive at Stack's company Web site. The official spoke on condition of anonymity to discuss an investigation still in progress.
The Web site featured a long note dated Thursday denouncing the government and the IRS in particular. It cited the Austin man's problems with the agency.
