LITTLE ROCK, Ark. (AP) -- The chairman of the Arkansas State Medical Board told paramedics that a tire exploded outside his home as he left to go to work, according to new details released in court filings about the blast that left the doctor seriously wounded.

Police and prosecutors previously gave few details about the February 2009 bombing that caused Dr. Trent Pierce to lose his left eye and suffer wounds to his face, neck, arms and legs.

Investigators believe a spare tire and rim were turned into a homemade bomb, which exploded as Pierce left his West Memphis home on Feb. 3, according to an affidavit by David Oliver, a special agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives.

"The investigators concluded that the perpetrator(s) utilized a military grenade and a vehicle tire and rim, to create an improvised explosive device," Oliver said in the affidavit, released this week.

Prosecutors say Dr. Randeep Mann of Russellville planned the attack to retaliate against the state medical board's disciplinary actions against him. The board stripped Mann of his right to prescribe narcotics after several of his patients fatally overdosed.

He has pleaded not guilty to all charges against him and faces a March 15 trial, though he is seeking a delay.

Mann, a licensed firearms dealer, was initially indicted for illegally possessing grenades a month after the bombing. That came after a city worker near his Pope County home stumbled upon a plastic-wrapped canister containing high-explosive grenades.

During a search of Mann's home, authorities found more than $1 million worth of weapons, though most were legally registered to him. Oliver's affidavit said investigators saw a spare tire - similar to what was used in the Pierce bombing - propped inside a glass-doored shower stall.

Authorities didn't initially seize the tire, but did in a search a few days later, court records showed.

A federal grand jury indicted Mann in the Pierce bombing earlier this month. He faces charges of using a weapon of mass destruction and the use of an explosive resulting in personal injuries, as well as conspiracy and obstruction charges. He is also accused of federal weapons charges, as well as possessing chloroform in his jail cell.

The affidavit, previously sealed, was attached to prosecutors' opposition to sever Mann's trial from that of his wife, Sangeeta Mann, who faces perjury and obstruction charges. Her attorneys have argued that linking her trial with her husband's would unfairly prejudice the jury against her and that the accusations against her are unrelated to those her husband faces.

Prosecutors opposed that, saying Sangeeta Mann's alleged crimes were linked to her husband's and that separate trials would be an unnecessary expense because much of the evidence is the same.

Judge Brian Miller hasn't yet ruled on the request for the delay or to sever the trials.

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