CHICAGO (CBS) – Authorities are trying to figure out how a local college student died, after her decomposing body was found in a Pilsen apartment this week, more than a month after she went missing.

Michelle Manalansan, a 29-year-old student at Harold Washington College, was last seen on Feb. 9, when she left her home in the 300 block of East South Water Street, wearing a pink jogging suit and white gym shoes.

On Sunday, police found her decomposing body in an apartment in the 1400 block of West Cullerton Avenue, about four miles away. Her body was inside a plastic air mattress that had been cut open and stuffed with garbage.

An autopsy performed on Monday was inconclusive, and police were continuing to investigate how she died.