The prisoner, identified as Shahzad (43) alias Baboo, a resident of Aligarh, complained of chest and abdomen pain on Wednesday, they said.
He was admitted to a hospital and died during treatment yesterday, police said.
Shahzad was an accused in a murder case lodged at the Delhi Gate police station in 2008.
In 2009, he was accused of helping a criminal in escaping from the custody of Aligarh police.
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