Constable Kerr was killed by a bomb under his car outside his Omagh home.
Brian Carron, 26, from the Dungannon area, was arrested in Scotland on 6 April and the 40-year-old man was detained near Omagh on 7 April.
Police were earlier granted a five-day extension to question a 33-year-old man arrested in the Omagh area last week.
Weapons and explosives, including four Kalashnikov rifles were found in the Coalisland area of County Tyrone on 5 April by police investigating the police officer's murder.
Mr Kerr's funeral witnessed unprecedented scenes - with police officers and members of the Gaelic Athletic Association uniting in his memory, as well as politicians from across all the main Northern Ireland parties.
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