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Marvin Heemeyer of Granby, Colorado was a profoundly frustrated muffler repair man. In the late 1990s⁠—after years of protests, petitions, and town meetings⁠—it became obvious to the 52-year-old that he was entwined in a gross miscarriage of justice. His business was ruined by some shady zoning changes, and Heemeyer contended that mayor and city council were corrupt. Even as he was forced to give up his legal fight and sell his land, he hatched one last plan to secretly retool his muffler shop to serve a single malevolent purpose: to construct a machine that would allow him to exact his revenge upon those who had wronged him.

Heemeyer first became enamored with the state of Colorado when he was stationed there in the Air Force. After his service ended, he moved to Grand Lake, Colorado and opened a small chain of muffler shops in the surrounding cities. After a while he began to lease some of the shops out to other operators, but kept one, Mountain View Muffler in Granby, to operate himself.

Heemeyer became involved with politics almost immediately upon establishing his home in Colorado. He was generally well-liked among his friends and neighbors, being described as an “enjoyable person,” and as someone who would “bend over backwards for anyone”. There were some, however, who were more familiar with his volatile temperament. He was a strong proponent of legalizing gambling, and he published at least two newsletters to disseminate his views. When a reporter for a local paper interviewed Heemeyer for an editorial opposed to gambling, he reported that Heemeyer was so enraged by the opposition that the interview nearly came to fisticuffs. In one particularly extreme instance, Heemeyer threatened to kill a customer’s husband when she refused to pay for a faulty muffler repair. “If Marv was your friend, he was your best friend,” said one of Heemeyer’s close associates, “but if he decided that he was your enemy, then he was your worst and most dangerous enemy.”

Marvin Heemeyer, welder and tinkerer

In the late 1990s the Docheff family approached Heemeyer to buy his one remaining muffler shop in order to build a concrete batch plant on the land. It was a matter of public record that Heemeyer had bought the land for $42,000. Docheff reported that they agreed to buy the land for $250,000, but the deal fell apart when Heemeyer raised the price to $375,000 and reportedly once even mentioned a million. Having grown weary of Heemeyer’s indecisiveness, the Docheffs went to the Granby City Council and sought to re-zone the land surrounding Heemeyer’s muffler shop.

Heemeyer was involved in the re-zoning process from the outset, attending town meetings to ensure that his interests were protected. Nevertheless, in 2001 the town zoning commission and trustees approved the rezoning request. Adding apparent insult to injury, the plan for the concrete plant cut off the only route to his muffler shop. The city also fined Heemeyer $2,500 for “junk cars” on his property, and for failing to have his shop hooked up to the sewer line.

Hindered but not yet defeated, Heemeyer set out to remedy the situation using community action, legal maneuvering, and elbow grease. He appealed the zoning commission’s decision, and gathered signatures from the townsfolk to petition against the plant. He attempted to obtain permission to install a sewer line under eight feet of land owned by Mountain Park Concrete, but the new owners refused. He even went so far as to buy a bulldozer to build a new road that would allow customer access to his muffler shop, but the city council declined to approve his plan. Many people suspected there were some shady dealings between the concrete plant and the members of the city council, but no actual evidence of such illegal goings-on has ever been found.

Having no recourse, Heemeyer sent the city a $2,500 check to cover the fines, with the word “cowards” written ominously on the memo line. He then sold the muffler shop property to a trash company, and was given six months to vacate.

One of several gunports inside the Killdozer

Heemeyer set to work on his new project almost immediately. The Komatsu D335A bulldozer that was meant to save his business was instead moved into the muffler shop, and Heemeyer began to make some modifications. He started by adding home-made composite armor⁠—cement sandwiched between thick sheets of steel⁠—to protect the cab, engine, and parts of the tracks. He installed front and rear cameras to feed images to monitors in the cab, and several gun ports were set around the control center. A stockpile of food and water was stored inside, as well as an air tank to help provide air circulation.

Throughout the one-and-a-half years of construction, Heemeyer documented his progress though notes and audio tapes. “Because of your anger, because of your malice, because of your hate, you would not work with me,” he stated in his tape recordings. “I am going to sacrifice my life, my miserable future that you gave me, to show you that what you did is wrong.” He received several visitors at his shop while working on his armored vehicle of vengeance, and none of them seemed alarmed at the weaponized armor shell atop his earth-mover. In his notes Heemeyer credited a higher power with “clouding their vision.” On one occasion he wrote, “I was always willing to be reasonable until I had to be unreasonable. Sometimes reasonable men must do unreasonable things.”

2004 was a tough year for Heemeyer. His father passed away in March, and he broke off his engagement when he caught his betrothed with another man. The morning of Friday, the 4th of June was gray and drizzly. Heemeyer mailed his audio tapes to his brother, went to his shop, and climbed into his bulldozer with a handwritten list of targets. He used the winch controls to lower the concrete and steel shell onto the top of his vehicle. Nothing short of a crane would be able to lift the thirty-ton armor shell off the vehicle once it was in place. With that fateful metal clap, Heemeyer was sealed in a concrete and steel box that he could never escape.

A truck smashed by the Killdozer

At just after 3:00 PM, the makeshift tank tore through the side of his shed, and smashed into the Mountain Park Concrete plant. Shortly thereafter, the phones at the 911 response center began ringing incessantly. A man named Cody Docheff witnessed the destruction-in-progress and attempted to use a front-end loader to intercept the rampaging bulldozer, but withdrew when he was fired upon from the gun ports of this “Killdozer.” Within minutes two buildings and multiple vehicles were eviscerated, and the Killdozer rumbled towards the highway into town. The slow-moving bulldozer picked up a parade of emergency vehicle escorts as it approached the city limits. One police SUV was crushed when it strayed too near.

Undersheriff Glen Trainor managed to climb atop the moving bulldozer, and used 37 rounds from his service pistol to try and shoot his way in. “I think the thing that drove me,” he later reported, “is that I knew that killing him behind the wheel was the only way we were going to be able to stop this thing.”

When Heemeyer and his Killdozer arrived in town, the Granby police were waiting for him. Against the armored behemoth, however, the lawmen were powerless. When it became clear that the armor was impervious to bullets the police tried explosives, but they too were without effect. Lawmen kept to the sides and tried to vacate anyone from the Killdozer’s path, and the local police utilized the reverse 911 system to call residents and warn them of the approaching danger. News helicopters filmed the unfolding violence from above.

The overencumbered vehicle was obviously difficult to control, and swerved widely through the streets, but Heemeyer was still able to seek out and and hit his specific targets. The bulldozer effortlessly demolished cars and buildings, including the home of a former mayor, the office of a newspaper that had sided against him in an editorial, the businesses of a former city councilman, and the city hall. Despite the destruction of property, no people had been injured or killed.

The remains of Granby city hall

The Granby Police requisitioned an industrial scraper to pit heavy equipment against heavy equipment, but the Killdozer merely shoved the lighter adversary aside.

In about an hour of mayhem, the bulldozer had demolished thirteen structures and was en route to its next target: Gamble’s Hardware. The damage from small arms and the extra weight of the armor were taking a toll on the vehicle, however. The radiator had sprung a leak, and the Killdozer was losing horsepower. As the fatigued machine crashed through the wall of the hardware store the floor beneath the beast broke, and the front end of the bulldozer fell into a shallow basement. The engine struggled, but it could not power itself out of the pit.

As SWAT teams surrounded the wounded Killdozer, one of the members reported hearing a single, muffled gunshot from within the cab. The vehicle didn’t move again, ending a rampage that had lasted 2 hours 7 minutes, and caused about $7 million in damage.

Explosives were employed to try to open the tank, but in the end it took twelve hours with an oxyacetylene torch and a crane to crack the armored top. Inside Heemeyer was found dead, having shot himself with a .357 handgun. He was the lone casualty of the destruction spree.

Today there are a number of groups which idolize Heemeyer and his fight against a corrupt system; celebrating his ingenuity, ambition, and his apparently valiant effort to prevent any casualties. But it is unlikely that Heemeyer himself deserves credit for the lack of serious injuries or deaths. Many of the buildings he razed were occupied moments before he attacked. There was also evidence of shots fired from the tank at multiple locales⁠—including one attempt to detonate a cache of propane tanks⁠—and a reported attempt to push a wall down onto a pair of police officers.

The steel beast bested by a shallow basement

Once the Killdozer’s cab was opened and Heemeyer was removed, the police inventoried his numerous guns, and found his list of targets; in addition to buildings and businesses, the list included names.

In order to prevent rampage admirers from collecting Killdozer memorabilia, the dozer was dismantled, and its parts were scattered among many separate scrapyards.

Anyone who has tried and failed to influence an uncaring government cannot help but feel a twinge of admiration for the extreme measures taken by Marvin Heemeyer. But while there is certainly a time and place for relentless, city-crushing machines, the line between legitimate vigilante and crazy-muffler-man-with-notions-of-divine-approval is much too fine for any one man to distinguish.