SALT LAKE CITY — One toxic gas, two dead little girls and a trio of frustrating smokescreens are inherent in a case that will play out in a federal courtroom beginning Friday, when a former pesticide applicator and the company he worked for have an initial appearance on separate three-count indictments.

Emergency responders are still shaking off the grief from the series of events that first began to unfold more than year ago on a quiet street in Layton. These events baffled police, firefighters and health department employees as they tried to uncover what led to the sudden hospitalization and death of a 4-year-old girl one day, and the hospitalization of her little sister the next.

New information shows how the mother appears to have done everything she possibly could to solve the puzzle of what was occurring at her home — and still, it didn't work.

What investigators believe and federal prosecutors now allege is that Coleman Nocks, 63, improperly applied Fumitoxin around the home where Rebecca Kay Toone, 4, and her sister, Rachel Ana Toone, 15 months, lived.

He and the company he worked for — Bugman Pest and Lawn Inc. — each have been charged with three counts of unlawful use of a registered pesticide stemming from the Toone tragedy and two other instances where investigators say Fumitoxin pellets were applied around homes in a manner "inconsistent with labeling."

The deaths of those two girls three days apart still resonate with public safety workers who had to piece together a puzzle that grew more complex with each passing hour — and the lessons learned are now being presented to anyone who will give one public health employee a listening ear.

"It was an impossible situation for everyone involved," said Dennis Keith, who is the bureau manager over emergency response and waste management with the Davis County Health Department. "What I told that family is I was going to do the best I could to educate people about this story and this incident to make sure this never happens again."

Keith was one of the presenters at a recent workshop at the state Department of Environmental Quality, where he and a state agriculture employee walked the audience through the timeline of the Layton Fumitoxen event.

It included information that hadn't been publicly released before. It's information designed to help those vested with safeguarding public health and safety realize that responses are more than just about keeping people on their toes — sometimes you have to get up on them and reach for the improbable.

It was the morning of Feb. 5 when Nocks showed up at the Toone residence to apply the Fumitoxin pellets to rid the area of an infestation of voles, small rodents that burrow in the ground.

Keith said federal restrictions in place at the time prohibited the placement of the pellets within 15 feet of an occupied residence. While 10 to 20 pellets about the size of a pencil eraser are recommended per burrow, the timeline draws on information from the company's invoice that says 1.2 pounds — or 907 pellets — were placed under a back-filled front porch pad and adjacent area. Fumitoxin is 55 percent aluminum phosphide, which reacts with water to produce phosphine gas, which is highly deadly and strictly regulated when used as a pesticide.

Five pellets, for example, produce 25 parts per million of phosphine gas, and it becomes "immediately dangerous to life or health" at 50 parts per million. It has since been banned by the Environmental Protection Agency for residential use and buffer zones have been expanded for other non-residential buildings that could be occupied by people or animals.

Fumitoxin has a garlicky or decaying fish smell. The girls' mother noticed the odor that same morning and questioned the applicator, and according to the timeline, was told it wasn't a problem, that it was "phosgene" gas that dissipates in the air.

By that afternoon, when the children got home from the school, the home's carbon monoxide detector was going off. Layton firefighters responded, and their detectors alerted them to carbon monoxide. When Questar showed up with a more-specialized monitor, Keith said carbon monoxide was ruled out.

"People were confused," Keith said. "They didn't know what was happening. Everyone thought it was an anomaly and people were talking about why things were not working properly."

The home was vented, there were no readings of gas, the fire department cleared the scene and the house appeared to be safe.

"Everybody did everything they were supposed to do," Keith said. "They (firefighters) left, there was nobody hurt and Questar had cleared the home of carbon monoxide."

Keith's timeline said the mother even placed a phone call to the pest control company to inquire about the fumigant and left a message without getting a reply.

Late that afternoon, he said she left to go to a professional conference, while the father took the girls out to eat at a local deli.

"The next day, everyone in the house is sick but the mother," Keith said. "That's another smokescreen in the case, because people start thinking it is food poisoning."

A visit to local pediatric medical clinic resulted in that diagnosis, which Keith said would not be uncommon because food poisoning can create flu-like symptoms.

But not long afterward, Rebecca Toone became unresponsive and was rushed to a hospital. Within hours, she died.

That initiated Keith's involvement in the case, as well as the police department. He said the fire department ordered everyone out of the house and the health department declared it unsafe to occupy.

By Sunday, Rachel Toone was hospitalized in guarded condition, and police contacted the Utah National Guard's 85th Civil Support team, made up of 22 members that include science and medical professionals. The team, stationed near Salt Lake International Airport, is specifically used in circumstances that require assessment of suspected nuclear, biological, chemical or radiological events.

They also carry sophisticated detection equipment designed to pick up the differing nuances of chemical hazards.

While strongly suspecting food poisoning as the culprit, investigators remained hampered by the Sunday closure of the deli and started to pursue alternative theories. Keith said the pesticide applicator was asked to return to the home and bring the invoice.

"We were told there was a possible fumigant and we wanted to know what was put down."

Keith said when the civil support team saw the invoice, they decided to test for phosphine gas — and it was confirmed.

"There can be some cross-sensitivity between carbon monoxide and phosphine," said the team's commander, Lt. Col. Tyler Smith. "Phosphine is not a common gas you find in places, but it is one of the most deadliest gasses that there are. That cross-sensitivity triggered the carbon monoxide detector, but nobody would ever suspect phosphine gas."

By Tuesday, an already severely poisoned Rachel Toone had died.

Keith said his presentations are not a finger-pointing demonstration aimed at any of the agencies involved. More than anything, they are designed to underscore the resources available and to stress the need for "redundancy" — that is overlapping responses and agencies backstopping each other to fill in the gaps.

"There were three huge smokescreens that hampered the investigation — it really was an impossible situation for every agency involved," Keith said.

Those smokescreens were: phosphine mimicking carbon monoxide and setting off detectors; symptoms similar to food poisoning; and what investigators say was too much product, too close to the home and no fumigant management plan left with the parents, who could have looked to it for guidance.

He said for him, it also drove home the need to impress upon other agencies the ability to tap the resources of the health department and be aware of deficiencies in detection equipment.

"It's my responsibility to tell that story," he said.

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Keith said he's been giving the presentation about once a month and has a couple of more planned before summer hits — when the use of pesticides increases.

"We may never see something as big as this ever again, but if we do, it is important that we are prepared, have the proper equipment and take the lessons learned from this," Keith said.

"We should be aware of our duty to protect lives every day and be vigilant," he said. "My big teachable moment is when that picture comes up of those little girls. Nobody wants to see that."