At least in the moment — and certainly in the 24 hours that followed — there was nothing ambiguous about the finish of the race. Dancer’s Image was a full 1½ lengths ahead of any other horse. Bets were paid out; trophies were distributed. The headline of the New York Times the next day blared, “Dancer’s Image Rallies to Win Kentucky Derby,” and The Washington Post put a photo of the victorious gray horse on Page 1 with the headline “Winner’s Image.”

But a race that’s supposed to last barely two minutes instead dragged out nearly five years before a victor was definitively crowned. In the 144-year history of the event, the 1968 race stands as the Derby’s lone drug scandal and the only time a winning horse was disqualified.

“Fifty years is a long time, but still today questions abound,” says Abby Fuller, whose father owned Dancer’s Image, the horse who was first across the line at the 1968 Derby and listed last in the official race records.

While Dancer’s Image was feted at the track, a bad drug test led to his disqualification and several years of legal wrangling. For many of the principals, the ensuing courtroom drama failed to produce answers, and the horse’s connections never understood how Dancer’s Image could fail a drug test. Was the testing bad? Had a medication that was authorized for training somehow not cleared his system? Or was it something more nefarious?

Peter Fuller, the horse’s owner, had a theory that many find just as credible a half-century later. In the weeks before the race, he had shown support for the widow of recently assassinated Martin Luther King Jr., which drew the ire of many during a tumultuous period in which racial tensions divided communities across the country. Did the charitable act by a New England horse owner inspire someone to sabotage Dancer’s Image in the days before the Kentucky Derby?

“I have no doubt,” his daughter says today.

In Louisville this weekend, 20 of the world’s best 3-year-old thoroughbreds will line up for a race that loves its history and usually celebrates its past. But don’t expect any remembrances of Dancer’s Image. Fifty years later, he’s the Derby’s forgotten, fallen champion.

“What we do know,” says Milton Toby, author of the book “Dancer’s Image: The Forgotten Story of the 1968 Kentucky Derby,” “is that on that day, he ran faster than any other horse in the Derby.”

Peter Fuller was so confident in his horse that he practiced the walk from his box at Churchill Downs to the winner’s circle ahead of time. Bettors had made Dancer’s Image the Derby’s second choice, at 7-2 odds. He had the pedigree (son of Native Dancer), the résumé (12 career wins — three more than any other Derby horse) and the jockey (Bobby Ussery had won the previous year’s Derby aboard Proud Clarion).

But Dancer’s Image also had ankle issues that cast doubt in the days leading into the race, and his handlers were being cautious.

“They maintained in the face of persistent rumors this week to the contrary that the colt would be fit and ready at post time,” The Post reported at the time.

Dancer’s Image received medication early in the week, and he completed his training runs. Then on race day, he got a bad break out of the gate. The horse was bumped and quickly fell 15 lengths off the lead.

But he slowly started moving through the field, weaving past the others. At the top of the stretch, Ussery slid the horse to the inside and passed the favorite, Forward Pass, at the eighth pole.

“I was too small to see it all with my own eyes,” says Abby Fuller, who was 9 at the time, “but I remember looking at the people around me — Mom, Dad, aunts and uncles — screaming and yelling. Dad saying, ‘Here he comes! Here he comes!’ ”

Dancer’s Image somehow went from last to first — just the fifth Derby winner at the time to do so. The horse was draped with a garland of roses, Fuller was handed a trophy, and everyone connected with the horse was still celebrating the next night when track officials got word that something was amiss.

Warner Jones, a longtime board member at Churchill Downs, called Fuller, according to a Los Angeles Times report, and said, “They’ve got a problem with your horse’s test.”

“What are you talking about?” Fuller responded.

“It’s very serious.”

Dancer’s Image had tested positive for a drug called phenylbutazone. At the time, the drug was legal to use in training but couldn’t be in a horse’s system on race day. Churchill Downs officials had no idea what to do.

“There’d never been a horse disqualified for a drug positive before then and never since. So nobody knew quite how to deal with that,” said Toby, a Kentucky author and lawyer.

They held a staff meeting to sort through their options. Kelso Sturgeon, the track’s public relations director at the time, once recalled to the Los Angeles Times that several officials argued against making public news of the positive drug test.

“They wanted to sweep it under the rug,” he said. “I started to tell [Wathen Knebelkamp, the president of Churchill Downs] that we couldn’t do that, that too many people already knew, when he cut me off.”

They made the unprecedented decision to declare the second-place horse, Forward Pass, the Derby winner. Dancer’s Image had gone from last to first on race day and was demoted back to last three days later.

Billy Reed was a sportswriter working at the Louisville Courier-Journal at the time and had just covered his first Derby. When the track’s decision leaked on a Tuesday afternoon, “it was absolute chaos in the office,” he said. “Nobody knew much about post-race urinalysis, all the procedures, what the chemist did. Everybody was caught completely off-guard. It was that way across the nation: Everybody was stunned.”

Fifty years ago, only the race’s winner and one random horse had to submit to a urine test. Trace amounts of phenylbutazone, commonly known as bute around the track, were found in Dancer’s Image’s sample. Bute is an anti-inflammatory used to alleviate pain, not a performance-enhancing drug.

“Bute’s not a stimulant or a depressant,” said Reed, the veteran turf writer. “It was more like an aspirin that humans take. To this day, probably over 90 percent of the race horses in the country use bute, sometimes only as a precaution.”

At the time, the drug was legal at many tracks but permitted only during training at Churchill Downs. Alex Harthill, the well-known equine veterinarian, gave Dancer’s Image a dose six days before the race to help his ankles, and it should have cleared within 72 hours. Dancer’s Image, everyone thought, had nothing in his system on race day.

“To the best of my knowledge, Dancer’s Image had not had any drugs of a prohibited nature,” Harthill told the New York Times.

As they processed the murky circumstances surrounding the lost victory, Fuller and the team around Dancer’s Image just couldn’t explain what had happened, their disappointment tinged with anger and confusion.

“The owner was mystified, the trainer had a squeaky-clean record — everybody was baffled,” said Toby, the author.

Seemingly no explanation made sense to Fuller and his connections — except maybe one.

Martin Luther King Jr. was killed in Memphis on April 4, 1968. Two days later, Fuller entered Dancer’s Image in the Governor’s Gold Cup race in Bowie, outside Washington, and won. Fuller quietly sent the race purse — more than $75,000 — to King’s widow, Coretta Scott King.

“It was just my way of saying, ‘Hell, this was a hell of a guy,’ ” Fuller once explained to the Boston Herald.

He didn’t publicize the gesture, and there were no splashy headlines. But the broadcaster Win Elliot caught wind of the donation and told the story on-air during the Wood Memorial.

The news wasn’t universally celebrated across the horse racing world and certainly not across all of Kentucky. During race week the previous year, King drew attention away from the Derby by demonstrating against housing discrimination in Louisville and staging a rally downtown. “I know that that hadn’t endeared him to the big shots back there,” Fuller later explained to the Los Angeles Times.

To many, Fuller was an outsider, a horse owner from New England who was making his first trip to Churchill Downs. He was a Harvard-educated, Boston auto dealer who was also the son of a former Massachusetts governor.

In the weeks leading into the Kentucky Derby, Fuller and his family received angry letters and death threats. His horse was derided around town with a racial slur, according to some reports, and back in New England, one of his stables was set on fire.

“We had this beautiful little barn across from our house in New Hampshire, and they burned it to a crisp,” Abby Fuller said.

According to Toby, Fuller reached out to Jones, the chairman of Churchill Downs at the time, to request additional security for his horse.

“Jones told Fuller that it wouldn’t be necessary because the track had ‘great security,’ ” Toby said. In actuality, the author said, “security was very lax. It would’ve been easy for almost anyone to get to the horse, if they wanted to.”

Fuller once described the track guard stationed at Dancer’s Image’s barn to the Associated Press as “an old fella sitting in a chair and asleep.” And so if someone was really that upset with the horse owner’s support of King’s widow, Fuller later theorized, why wouldn’t they come after his horse?

“I’ve always wondered if what happened to the horse could have come in retaliation for my support of King,” Fuller told the Los Angeles Times.

Fuller had been an amateur boxer and wrestler back in college, so he had little interest in backing away from a fight. He took the Kentucky State Racing Commission to court, eager to restore the Derby win and his horse’s reputation.

Dancer’s Image won the first round when a Kentucky county judge said the commission’s disqualification was based on evidence “lacking in substance.” But they’d lose the ensuing appeals. Fuller’s legal fees ballooned and soon topped the Derby’s $122,000 prize money. In April 1973, Fuller threw in the towel. The 1968 Kentucky Derby was finally over, nearly five years after it began.

Less than a year later, Kentucky’s racing commission agreed to legalize phenylbutazone.

Dancer’s Image ran just once more, finishing third at the Preakness, which was won by Forward Pass. But he was quickly disqualified for bumping another horse and dropped to eighth. Fuller retired his horse shortly after. Dancer’s Image was eventually sold and enjoyed a long stud career overseas before dying in 1992.

Fuller was 89 when he died in 2012. He remained in the horse business for years but never had another Kentucky Derby contender. The controversy always ate at him.

“For him, it was always still there,” his daughter said. “He could never just let it go, I guess, because he never understood what exactly happened. We just never knew the full story.”

More than 150,000 people will attend this year’s Kentucky Derby, many filing right past the Kentucky Derby Museum on the Churchill grounds. The museum features a giant timeline that lists Forward Pass as the 1968 winner. The race results list Dancer’s Image first with an asterisk noting he was disqualified. There are no artifacts related to that race on display.

Fifty years later, the first horse across the finish line is the last one many want to remember.

“That’s by design,” said Reed, the veteran Louisville sportswriter. “Obviously that was an embarrassment to Churchill Downs, to the Kentucky racing industry. Nobody wants to talk about it. I’m not surprised they’re not doing anything official to honor his memory because I think they’ve always wished it’d just go away.

“To me, Dancer’s Image will always be the winner of that Kentucky Derby. I thought he was the best horse on the track that day. All the stuff that happened later was just a complete comedy opera of sorts.”

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