The House Subcommittee on Oversight and Investigations has heard on Tuesday testimonies from both the families of victims of tainted heparin and the U.S. Federal Drug Administration. The drug regulator said that it believes that contamination of the blood thinner heparin which led to 81 deaths was deliberate.

"FDA's working hypothesis is that this was intentional contamination, but this is not yet proven," Dr. Janet Woodcock, director of the agency's drug center, said in written testimony. The hypothesis was backed by Baxter International Chief Executive Robert Parkinson, who also said his company was "alarmed that one of our products was used in what appears to have been a deliberate scheme to adulterate a life-saving medication".

At the same time, families of victims which fell to tainted heparin have told heartbreaking stories of the last moments in the lives of their loved ones.

LeRoy Hunley of Toledo, Ohio, described how he lost both his 65-year-old wife and his 47-year-old son within weeks of each other. Both were suffering from a genetic kidney disease that required constant dialysis, for which heparin is routinely used.

Colleen Hubley, a dialysis nurse, was also present at the hearing on Tuesday. She recounted how her husband, Randy, came home from a dialysis treatment experiencing diarrhea, abdominal pain and breathing problems. He died the following night after she desperately tried to save his life with cardiopulmonary resuscitation

Contaminated heparin has been connected to 81 deaths and 785 severe allergic reactions, according to Rep. Bart Stupak, D-Mich., chairman of the House Energy and Commerce subcommittee on oversight and investigations.

Heparin, made from ingredients extracted from pig intestines, is used to prevent blood clots in millions of people with heart conditions, kidney disease and in surgery. Baxter International Inc. sold the heparin involved in the reported deaths. The company initially recalled nine lots of its product in February, after receiving hundreds of reports of allergic reactions possibly linked to heparin.

Shortly after, the company recalled all remaining heparin products. A FDA investigation revealed that the heparin was contaminated with a man-made chemical compound known as over-sulfated chondroitin which is cheaper than heparin, but mimics it. FDA said that Changzhou SPL, a Chinese subsidiary of Scientific Protein Laboratories, is the source of the contaminated heparin.