BERKELEY (CBS SF) — A Berkeley couple found dead in their apartment under mysterious circumstances last week died as a result of acute carbon monoxide intoxication in what’s being described by police as a “tragic accident.”

The bodies of Roger and Valerie Morash and their two cats, were found in their apartment in the 3000 block of Deakin Street on Jan. 23.

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Investigators reviewed autopsy findings, toxicology reports and necropsies of the dead cats to make the determination. They also collected items around the apartment to test them for the presence of presence of toxins, finding none.

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They are still trying to determine the source of the carbon monoxide.

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