Ellen Greenberg was found dead in her apartment with 20 stab wounds back in 2011.
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The medical examiner's office initially ruled her case a homicide, but then later changed it to suicide.
Greenberg's family has long sought to get her suicide ruling changed to homicide or undetermined.
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In the lawsuit, the Greenberg family alleges the city conspired to cover up Ellen's murder.
A city spokesperson said they do not comment on pending litigation.
SEE ALSO: Chester County DA will investigate 2011 death of Manayunk teacher ruled suicide
Chester County DA will investigate death of Manayunk teacher ruled suicide