A Florida pharmacy that mixed a deadly concoction of vitamin supplements that killed 21 elite polo horses belonging to a Venezuelan team fired a lab technician who prepared the mix after she spoke with federal investigators, according to a complaint filed against the business.

Sheila Harris, of Ocala, Florida, claims she cooperated with Food and Drug Administration investigators in the weeks following the deaths, and her employer, Franck's Pharmacy, then fired her for talking about the case.

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"Regardless of what it was that caused the (horses') deaths, she was retaliated against for providing accurate information, complete information to government investigators," Harris' attorney, Thomas Wade Young, said Friday.

The complaint, filed July 16, seeks reinstatement, unspecified compensatory damages and reimbursement for lost wages.

Franck's denied the allegations in a statement to The Associated Press.

"Franck's Pharmacy has been cooperating completely with the authorities since the very first moment it learned of the polo tragedy," the statement said. "Franck's did not dismiss the employee for cooperating with investigators. In fact, we have consistently encouraged all of our employees to cooperate fully with investigators."

The FDA and Florida authorities are still investigating while Franck's Pharmacy continues to do business.

Florida's state veterinarian, Dr. Thomas J. Holt, has blamed the horses' deaths on an overdose of a common mineral that helps muscles recover from fatigue. Holt said in April that toxicology tests showed significantly increased selenium levels.

The horses from the Venezuelan-owned Lechuza Caracas team began collapsing April 19 as they were unloaded from trailers at the International Polo Club Palm Beach before a championship match. Some died at the scene as spectators watched in horror; others died hours later. The horses had been given the supplement that day.

Franck's Pharmacy has acknowledged the concoction contained too much selenium. The Lechuza team had ordered a compound similar to a name-brand supplement known as Biodyl, which includes vitamin B, potassium, magnesium and selenium. The supplement is used around the world but has not been approved by the FDA in the U.S.

Harris claims she worked for Franck's for more than 13 years. She said she mixed the compound as ordered but later noticed "its consistency had changed, and the liquid had become cloudy."

The complaint alleges Harris was told by a pharmacy manager to simply "adjust the Ph balance and to filter the drug again."

It was then labeled and delivered.

Harris claimed she spoke with FDA investigators twice after the horses died. She said she was fired May 14, the day before an FDA investigator was set to return for a third interview.

Franck's Pharmacy contended in a termination letter to Harris, included in the complaint, that she was fired "as part of a company-wide effort to improve performance and increase efficiencies," not for misconduct.