Austin, Texas (CNN) -- The former accountant for Andrew Joseph "Joe" Stack III -- who officials say flew his plane into a Texas building housing an Internal Revenue Service office -- says Stack had never threatened him, a spokesman for the accountant said.
CPA Bill Ross was mentioned in a 3,000-word message on a Web site registered to Stack, which railed against the government, particularly the IRS. The online message believed to have been written by Stack criticizes accountant Ross for "representing himself and not me."
Ross had not heard from Stack since October, when his client "disengaged" services in a letter, spokesman Chad Wilbanks told CNN. According to Ross, Stack had not expressed any threats toward the accountant or the IRS, Wilbanks said.
"Mr. Stack contacted my firm to help with his personal taxes in 2008. He failed to provide me with all his income and other information resulting in an IRS audit," Ross said in a written statement Saturday. "Unfortunately, Mr. Stack ignored the audit and my advice which only complicated his situation, at which time our firm disengaged our services with Mr. Stack whom we have not been in contact with since October 2009."
Video: What Stack's writing reveals
Video: Crash victim's son speaks
Ross did not provide any further details in the statement on his work with Stack. Wilbanks said Ross, who has worked as a CPA for at least 30 years, thinks Stack located him in the phone book. They only met four times and did not have a personal relationship, Wilbanks said.
The FBI has taken over the investigation into the crash, and Ross has spoken to investigators, Wilbanks said. While Ross does not fear for his safety, he has "taken precautions," though those steps were not detailed by Wilbanks.
The online message, in a hit to the IRS, states, "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.
"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."
Read the apparent suicide note (PDF)
The seven-story building attacked in northwest Austin held offices for nearly 200 IRS workers. Two people were killed and two others were hospitalized when Stacks crashed his plane into the building Thursday, federal officials said.
One of the injured, Shane Hill, announced his release from the hospital Saturday.
"I am very grateful to the first responders who were there to assist me, and to those who have cared for me in San Antonio," Hill said in a written statement. "I am so blessed to be home today, and I ask for your courtesy and our privacy as my family and I focus on making a quick and full recovery."
Though the remains of two people found in the IRS building have been identified, their identities will not be revealed until after a forensic examination, said Ralph Diaz, special agent in charge of the FBI's San Antonio field office.
Watch one of crash victim's sons say he's "still a little shocked" 
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 the Piper Cherokee PA-28 had several seats removed and a fuel drum was missing from the airport Stack took off from.
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.
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.
Like Ross, friends and former colleagues 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."
CNN's Tracy Sabo contributed to this report.
