WEST VALLEY CITY, Utah -- It began with bullets and bloodshed one November afternoon. A 21-year-old woman was dead. Two undercover officers had opened fire on her car. The police began asking the usual questions about what had happened, and why.
Their investigation cracked open what one prosecutor called a "Pandora's box of problems" here in Utah's second-largest city, where Mormon pioneers once raised milk cows and sugar beets. There have been accusations of stolen drugs and missing money, abuses of police power and a cloud of corruption that defies Utah's reputation for sunny optimism.
Over the past few months, accusations of bad police work in the narcotics squad of the West Valley City Police Department have engulfed the town and sent shock waves through Utah's justice system. Prosecutors have tossed out 125 criminal cases. Dozens of convictions may have to be re-examined. The F.B.I. is investigating the Police Department and several officers.
Officials in Utah say they have never seen anything like it.
"Chaos," said Sim Gill, the district attorney for Salt Lake County.
And West Valley City, a diverse blue-collar suburb of about 132,000 people that has tried to overcome its image as the state capital's scraggly stepchild, has been knocked on its heels. Instead of discussing new office parks and glimmering shopping malls, city officials are facing a drumbeat of negative news coverage. The city is now likely to face lawsuits from people whose drug arrests have been undermined by accusations of police misconduct.
"As you start to put these things together, each one individually is concerning," Mr. Gill said. "Collectively, they are devastating."
The uproar began with the killing on Nov. 2 of Danielle Willard in the parking lot of a run-down apartment complex.
Ms. Willard, who had struggled with drug addiction for much of her life, was shot and killed by undercover officers from the West Valley City Police Department's neighborhood narcotics unit. The police say that Ms. Willard had been seen buying drugs, and that when officers approached her silver Subaru Forester, she backed up in their direction, striking one officer. They opened fire, hitting her in the head. She was unarmed.
As police investigators combed through the crime scene, they popped opened the trunk of the car belonging to Detective Shaun Cowley -- one of two narcotics officers who had been on the scene of the shooting. Inside, they found drug paraphernalia and items linked to previous drug cases. The discovery touched off an investigation into the actions of Detective Cowley and the other officers in the unit.
Lindsay Jarvis, a lawyer for Detective Cowley, said that the evidence found in his car was in sealed, marked bags in a lockbox. "Was there something criminal about it? Absolutely not," she said. "Shaun is being used as a scapegoat for all of the activities going on in the narcotics unit."
In a department with about 180 officers, the neighborhood narcotics unit was a squad of seven officers, one sergeant and one lieutenant that focused on smaller-scale dealers and users, according to Anita Schwemmer, the acting police chief. The unit handled hundreds of cases each year.
As weeks passed with little information about Ms. Willard's killing, questions multiplied. Ms. Willard's family seethed, publicly calling West Valley City's silence a cover-up. Articles in The Salt Lake Tribune raised questions about the department's policies, and people started asking whether West Valley City's residents could still trust its police force.
"It really heated up," said Wayne Pyle, the city manager.
Over the winter, West Valley City's retiring police chief shut down the narcotics unit, leaving drug arrests to patrol officers and other departments. The unit's nine officers were put on administrative leave. And last month, West Valley City officials offered a few details from their investigation into the drug squad.
They found that officers had mishandled evidence and had placed tracking devices on suspects' cars without getting necessary warrants. Confidential informants had been misused. In some cases, officers had removed trinkets like necklaces or candles from the scene of drug arrests as "trophies." In a few instances, drugs and money were missing.
City and police officials say the problems appear to be confined to the narcotics unit, and said most of the missteps were relatively minor, like taking change or DVDs from seized cars that were bound for the auction block. Officials said that only a few officers appeared to have a hand in the most serious breaches.
"Do I believe it's widespread corruption up and down the department?" Mr. Pyle, the city manager, asked. "No, I do not."
Whatever its scale, the revelations upended scores of criminal cases.
After Joseph Hu, a network engineer and part-time student, was arrested on charges of drug distribution and weapons possession last September, his lawyer filed a request for West Valley City to test the $40 in heroin they claimed to have seized. A few weeks later, the city dismissed the case with no explanation and let Mr. Hu out of jail.
"All we knew was something was wrong," said Mr. Hu's lawyer, Kelly Ann Booth. "But we didn't know what."
The pattern was repeated in case after case, defense lawyers said: When they decided to challenge drug charges rather than accept a quick guilty plea, West Valley City folded up the cases. Then the district attorney, after reviewing hundreds of cases, began dismissing them by the dozen, saying he could not successfully prosecute them.
"There was not a single case I wanted to dismiss," Mr. Gill, the district attorney, said. "We had no choice."
Advocates for Hispanic residents were jarred by one detail: In 93 of 114 cases, dismissed by the district attorney, the defendants had Latino last names. City officials say that reflected a reality of how drugs are traded and trafficked in central Utah; activists said it indicated bias.
"This is racial profiling all the way," said Tony Yapias of Proyecto Latino de Utah. The group has been meeting with city officials as they try to rebuild bridges in the community.
So far, no criminal charges have been filed against anyone in the department, and no officers have been fired.
In Washington State, Ms. Willard's mother, Melissa Kennedy, said she is getting tired of waiting. Her daughter, she said, was a goofy and bubbly girl who was falling into a heroin addiction by the time she was a high school senior. Her parents had sent her to Utah to a rehab program near Salt Lake City. It seemed to work for a while, but Ms. Willard fell back with friends who were drug users.
Ms. Kennedy said she does not know whether her daughter had started doing drugs again, but she said she was a 21-year-old who should still be alive. Ms. Kennedy has filed a federal civil rights lawsuit against the city.
"I've been lied to, my daughter has been murdered and I don't know why," Ms. Kennedy said. "There is not one thing they could say to me that I would believe."
This article originally appeared in The New York Times.