The minor girl, belonging to a poor family in Kalamassery near here, was sexually abused by her father's drunkard friends at her house while she was recuperating from meningitis, they said.
The girl who fell ill after the incident was admitted at Government Medical College Hospital, Kottayam, for getting special medical care, police said.
Police suspect that the infection caused due to the assault could be the reason for the death.
Based on a complaint filed by childline activists, Kalamassery police had arrested Ravi (49), Raju (36) and Rajesh (31) in September for their alleged role in the crime.
Kalamassery police has registered a case under relevant section of CrPC after the girl's death.