Austin, Texas (CNN) -- A man accused of flying a small plane into an Austin building housing an Internal Revenue Service office last week was one of two people killed in the incident, Texas authorities confirmed Monday.
The man who authorities say was the pilot, Andrew Joseph "Joe" Stack III of Austin, and Vernon Hunter of Cedar Park have been identified as the two people killed Thursday, according to the Travis County medical examiner's office.
Both men died from blunt force injuries, said Sarah Scott, chief administrative officer for the medical examiner.
Authorities say that on Thursday, Stack flew a single-engine plane into a seven-story building that held offices for nearly 200 IRS workers. Two other people were hospitalized.
Hunter and his wife, Valerie, worked at the IRS office in the building, his brother Harold L. Jackson told CNN affiliate WAAY. Hunter spent the past 15 years as a collections agent and previously served 22 years in the Army.
Jackson said Hunter was the youngest of five brothers. Hunter was adopted as an infant and kept his birth name into adulthood.
"We called ourselves the Jackson Five, the other Jackson Five," Jackson said.
Agents were looking into whether the seats of the plane were removed to accommodate a fuel drum in an effort to cause maximum damage, an official familiar with the investigation said Friday.
The official, who could not speak on the record because of the ongoing investigation, said that the Piper Cherokee PA-28 had several seats removed and that a fuel drum was missing from the airport where authorities say Stack took off.
The single-engine plane has a fuel tank capacity of 38 gallons and is equipped with four seats, according to the Web site risingup.com.
Authorities say Stack also torched his $230,000 home in Austin on Thursday morning before embarking on his fatal flight.
A 3,000-word message on a Web site registered to Stack railed against the government, particularly the IRS.
"I saw it written once that the definition of insanity is repeating the same process over and over and expecting the outcome to suddenly be different," the online message says. "I am finally ready to stop this insanity. Well, Mr. Big Brother IRS man, let's try something different; take my pound of flesh and sleep well."
Stack's wife, Sheryl Stack, expressed her "sincere sympathy to the victims and their families" in a statement read by family friend Rayford Walker on Friday.
Friends and former colleagues have said they had no inkling of the rage apparently building inside Stack.
"He hid that very well," said Billy Eli, in whose band Stack played bass until a few years ago. "Obviously, he was in some serious distress and had some real despair. I never saw that."