The software engineer who crashed his plane into an office building that held more than 200 federal tax agency employees may have removed seats from the aircraft to make room for extra fuel to cause the most destruction, according to a published report.
A law enforcement official familiar with the investigation in Austin told CNN that several seats were missing from Joseph Stack's Piper Cherokee PA-28 and a fuel drum was also missing at the airport from which he took off Thursday.
"I think there is a good chance he might have put it on his plane," the official said.
LIVESHOTS: Victim in Austin Plane Crash Identified
Stack took off from Georgetown Municipal Airport, about 30 miles from Austin, at 9: 40 a.m. ET and flew low over the Austin skyline before plowing into the side of the Echelon 1 office building just before 10 a.m. ET. Flames shot from the building, windows exploded and terrified workers rushed to get out.
Stack's wife said Friday she is sorry for everyone affected by the tragedy, The Associated Press quoted a family spokesperson as saying.
Rayford Walker said he's a spokesman for Joseph Stack's family. He read a statement from Stack's wife, Sheryl Stack, while standing in front of a house across the street from the Stack home. The Stack home was set on fire Thursday before Joseph Stack crashed his plane into the building.
In the statement, Sheryl Stack thanks her friends and family and offers her "sincerest sympathy" for the victims and their families. She also says she won't comment further.
Authorities say Joseph Stack III was angry with the government and crashed his plane into the building. He killed himself and one person in the building.
SLIDESHOW: Small Plane Crashes Into Austin Office Building
Stack left behind a rambling anti-government manifesto, but otherwise offered little indication that he was planning such an attack.
The National Transportation Safety Board (NTSB) has transferred control of the investigation to
the Federal Bureau of Investigation.
A. Joseph Stack III posted his angry screed on a Web site registered to him before he flew a single engine plane into the hulking black-glass Echelon 1 building on Thursday, killing himself and at least one worker. Stack, 53, apparently targeted the building's lower floors, which housed local offices of the Internal Revenue Service.
An IRS worker, Vernon Hunter, 67, was killed in the crash. Vernon was a Revenue Office Manager responsible for collections. His wife Valerie also works for the IRS and was in the building when the plane struck.
On Friday, police and fire investigators picked through the wreckage at the office building and at Stack's red brick home about six miles away — which Stack apparently set fire to before taking off his his plane. The home's roof had caved in and its windows had blown out.
Click to read the "manifesto" published on Stack's Web site.
U.S. law enforcement officials also said they were trying to determine if Stack put anything in the plane to worsen the damage caused by the impact and fire.
In his self-described "rant," Stack railed against "big brother," the Catholic Church, the "unthinkable atrocities" committed by big business and the governments bailouts that followed.
In the note, signed "Joe Stack (1956-2010)" and dated Thursday, he said he slowly came to the conclusion that "violence not only is the answer, it is the only answer."
Click for chilling eyewitness accounts of Texas plane crash.
Click here to watch video of Joseph Stack playing in a band.
Law enforcement officials, speaking on condition of anonymity because the investigation was still going on, said Stack apparently posted the screed and set fire to his house before leaving for the airport.
Some who knew Stack said he offered little hint of his anger.
"He didn't rant about anything," said Pam Parker, an Austin attorney whose husband played in a band with Stack. "He wasn't obsessed with the government or any of that. ... Not a loner, not off in a corner. He had friends and conversation and ordinary stuff."
But in his posting, Stack fumed about the IRS and wrote, "Nothing changes unless there is a body count."
"I have had all I can stand," he wrote, adding: "I choose not to keep looking over my shoulder at `big brother' while he strips my carcass."
Federal Aviation Administration spokesman Lynn Lunsford said Stack didn't file a flight plan.
The Pentagon scrambled two F-16 fighter jets to patrol the skies over the burning building before it became clear it was the act of a lone pilot, and President Barack Obama was briefed.
Click for more from MyFoxAustin.com.
The Associated Press contributed to this report.
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