Ivor Bell, widely reported to have been an IRA commander in Belfast during the 1970s, was arrested in a raid on his home in Andersonstown on Tuesday.
Police from Serious Crime Branch have been given until Friday night to continue interviewing the suspect at Antrim Police Station.
37-year-old Mrs McConville, a widow and mother of 10 children, was abducted in December 1972 from her flat in the Divis area of west Belfast and shot by the IRA.
Her body was recovered on a beach in Co Louth in August 2003.
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