Obaid-ur Rehman was shot dead when he was trying to escape the police custody in Altaf Nagar area of Orangi Town, Dunya TV reported.
During a press conference yesterday he had confessed to killing 22 people, held by Deputy Inspector General of Police (DIG) Tahir Naveed.
The police was quoted as saying by the news channel that the suspect snatched weapon from a policeman and opened fire, injuring a constable.
DIG Naveed has said that the suspect had confessed to killing 22 people including four doctors and eight constables.
Police are also conducting raids in different areas to nab accomplices of the Obaid.
Karachi, Pakistan's financial capital, has wrestled for several years with a bloody wave of criminal, sectarian and political murders, forcing the authorities to launch a targeted operation across the city to tackle criminal elements.