FONTANA (CBSLA) — Investigators were at a home in Fontana on Friday night trying to determine how two middle-aged people died inside the home.

A preliminary investigation suggested a man and a woman died from an overdose of the powerful painkiller Fentanyl, officials said.

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KCAL9’s Tina Patel reported from the 14300 block of Arrow Boulevard, where she said many neighbors had never even heard of the powerful drug.

The DEA was trying to determine what drugs might have been involved.

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Relatives had come to check on the two. A third woman was also found in the home unconscious, and she was taken to a hospital. Her condition was unknown, Patel reported.

There were also several children in the home. They appeared to be fine, officials said, but were checked out as a precaution.

“Not too many people are aware of how deadly it is,” said Fontana Police Officer Jay Sayegh. “I mean, the smallest amount — that’s why our officers were taking such precaution. It’s not every day we need a hazmat crew have to go into a residence. Simply breathing in the smallest amount can result in death.”

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If the substance does turn out to be Fentanyl, officials said there will be a lengthy process to clean it up and decontaminate the scene.