 Story highlights Chemical damages ozone and is being phased out, though it's used in strawberry fields, EPA says 
 
 A Delaware family becomes ill at a resort in the U.S. Virgin Islands 
 
 Preliminary EPA results find methyl bromide was present in the unit where they stayed 
 
 (CNN) A Delaware father is in stable condition and improving as his two boys remain in critical condition after they became sick -- perhaps from pesticide exposure, federal officials say -- during a trip to the U.S. Virgin Islands. Steve Esmond, his teenage sons and the teens' mother fell ill more than two weeks ago in St. John, where they were renting a villa at the Sirenusa resort. The family has confidence in their medical professionals and is hopeful for a full recovery, according to a statement released Monday from the family's attorney, James Maron. A family spokesman said Steve Esmond, his wife, Theresa Devine, and their two teenage sons were airlifted to hospitals on the U.S. mainland. The U.S. Environmental Protection Agency said Friday that the presence of a pesticide at the rented villa in St. John may have caused the illnesses, which were reported to the EPA on March 20. JUST WATCHED Banned pesticide allegedly sickens family at resort Replay More Videos ... MUST WATCH Banned pesticide allegedly sickens family at resort 01:37 PLAY VIDEO 
 
 Esmond was found unconscious; the boys and their mother were having seizures, Maron said. Elias Rodriguez, an EPA spokesman, said the agency's preliminary test results "do show that there was a presence of methyl bromide in the unit where the family was staying." Exposure to methyl bromide can result in serious health effects, including central nervous system and respiratory system damage, according to the EPA. "Certified pesticide applicators know this is not approved for indoor residential use," Enck said. Use of the pesticide was confirmed the day after the family became ill, which has helped inform doctors on how to treat the family, said Judith Enck, the EPA's regional administrator in New York City, which has jurisdiction over the U.S. Virgin Islands. Banned in many places 
 
 Dr. Sanjay Gupta, CNN's chief medical correspondent, said many parts of the world banned the chemical, a neurotoxin. The chemical is often mixed with tear gas so people can be aware of its presence, he added. Initially, the EPA had said methyl bromide had been used in more than one apartment in March. Sea Glass Vacations, which acts as a rental agent for several units at Sirenusa, said the unit directly below the one where the family stayed was recently treated for pests, but that the family's unit was not treated. The company said it licensed an outside company, Terminix, for the pest control services. The United States Department of Justice has also opened a criminal investigation into the case, according to a Securities and Exchange Commission report filed by ServiceMaster Global Holdings, Inc., the parent company of Terminix. The attorney added: "The family is confident that the responsible parties will be brought to justice and held accountable."
– A Delaware family that became seriously ill in the US Virgin Islands was poisoned by an odorless and highly toxic pesticide that should never have been used indoors, according to Environmental Protection Agency investigators. Methyl bromide was used to fumigate a unit at the Sirenusa resort on St. John days before the family was hospitalized on March 20. It was also "used in other apartments around the same time that it was applied here, and also in different apartments in the complex within the past year," an EPA official tells NBC News. Weeks after they became ill, two teenage boys are still in critical condition after being airlifted to a hospital on the US mainland; their father is in stable condition. "We have confirmed that the problem is indeed methyl bromide," which was banned from indoor use in the US—including the Virgin Islands—decades ago, an EPA official tells the AP, describing the gas as a "potent neurotoxin" that "can cause convulsions, coma, cognitive deficits, inflammation of the lungs." The Justice Department has begun an investigation and Terminix, the pest control company involved, says it is cooperating, CNN reports. "Many questions remain why an odorless pesticide of this level of toxicity could be manufactured, distributed, and applied in a residential area resulting in this family's injuries," the family's lawyer said in a statement.