CUMMING - Over the past 18 months, Forsyth County Sheriff's deputies had been aggressively training for the exact scenario that unfolded Friday morning when a heavily armed man attempted to storm the county courthouse in downtown Cumming.

"If not for the actions of the deputies that work in that courthouse, particularly the one who was outside who got shot, we would have had severe loss of life," said Sheriff Duane Piper. "[The gunman] came there ... with the specific purpose of killing as many people as he could. The actions of the deputies saved several lives."

The attack set off a firefight that wounded one deputy and ended in the death of the gunman, a 48-year-old Cumming man who reportedly had grievances with law enforcement.

According to the sheriff's office, Dennis Ronald Marx was scheduled to appear in court that morning to enter a guilty plea on drug and weapon charges from August 2011. He never made it inside.

Instead he launched an attack that Piper, citing the number and construction of devices found in Marx's home and a vehicle outside the courthouse, appeared to have been months in the making.

"He came prepared," Piper said. "It was very close to being a major catastrophe."

The sheriff added, though, that there is "no indication that [Marx] was working in concert with anybody else before or during [it]. He was by himself."

In addition to the injured deputy, Piper said eight other deputies shot at Marx. All have been placed on paid administrative leave, a standard practice for officers involved in a shooting.

According to Piper, Marx drove a rented silver Nissan Armada onto the courthouse plaza about 9:57 a.m. and threw out spike strips to hold off law enforcement's response before beginning a "full frontal assault" on the facility.

"It appeared he was trying to actually drive through the front of the courthouse," Piper said. "We had a court security deputy who was outside at the time ... it looks like he saw that deputy, swerved toward him to try to run over the deputy and the deputy engaged him."

The deputy, later identified as Daniel Rush, approached Marx, who began firing at him through the window of his sport utility vehicle at the courthouse steps.

Piper praised Rush, a 30-year-veteran of the force who underwent surgery Friday night to repair two broken bones in his leg and is expected to make a full recovery, as the reason there were no other injuries. "The entire situation was solved by that deputy," he said.

Shortly after Rush encountered Marx, the county's SWAT team, which just happened to be nearby, and deputies from the jail and courthouse joined in the firefight.

Marx, who was alone in the vehicle and wearing body armor, was struck several times and died at the scene.

Piper said two of the eight deputies had assault rifles, with the majority firing pistols. Marx was shooting into the courthouse, where deputies posted inside returned fire.

"The deputies actually took the time not just to stand right there at the front door, but they actually went into other offices and broke windows and were shooting from different places inside the courthouse to get different angles on him," Piper said.

Marx was heavily armed as he approached the courthouse.

"He was throwing tear gas, grenades, he was throwing smoke grenades, pepper spray grenades and he also had a gas mask on," Piper said. "... He also had flex cuffs ready to apply to people."

The sheriff was clear that if Marx had made it into the building, lives would have been lost. "He came there with the purpose of occupying the courthouse," he said.

While the gunfire lasted about three minutes, it was hours before downtown Cumming was cleared, as multiple explosives were thought to be at the scene.

The courthouse, Forsyth County Administration Building, Cumming City Hall and surrounding structures were evacuated quickly and later closed for the day. Traffic was rerouted.

At least one person, described as an older man, was taken to a hospital after he fell while leaving a building downtown. No other injuries were reported.

Piper noted that Marx, who was no stranger to law enforcement, had a home on Lakeside Trail east of Cumming and near Lake Lanier, though he had not been living there for at least 10 days.

According to court documents, Marx was suing the sheriff's office alleging civil rights violations, including excessive force.

According to court records, Marx faced many drug-related charges from August 2011, including manufacturing marijuana, possessing a firearm or knife during the commission of a felony and possession with intent to distribute.

The sheriff's office, Georgia Bureau of Investigation and Bureau of Alcohol, Tobacco and Firearms worked the scene downtown, though they determined within a couple of hours that there was no further danger to the public.

As a precaution, they canvassed the area around the courthouse for any possible explosives. They also searched Marx's home and the hotel off Market Place Boulevard where he had been staying.