Updated 06/27/14 – 2:18 p.m.

CHICAGO (CBS) — A young mother who had been missing since Monday was found dead in a Garfield Park garage on Thursday, along with a 31-year-old man. Authorities said they died from carbon monoxide poisoning.

Nicolette Medina, 25, and Marco Acevedo, 31, were found dead around 3:30 p.m. Thursday in a garage in the 3800 block of West Gladys Avenue.

Police said Medina was last seen on Monday, when she left her home in the 3700 block of West Lawrence Avenue. She told her roommate she would return, but never came back, according to a missing person alert from Chicago Police. She had not been answering her cell phone and had not contacted her family since she left home.

Autopsies conducted on Friday determined Medina and Acevedo died from carbon monoxide intoxication from automobile exhaust, due to being inside a running car in a closed garage. Their deaths were ruled accidental.

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