Freddie Scappaticci was Britain's most highly prized IRA informant.
His codename was 'Stakeknife' and the unit he led - ironically in charge of hunting informants like him - was called the 'nutting squad' as it shot people in the head after abducting and torturing them.
Scappaticci never faced trial and lived under witness protection in England until his death last year, aged 77.
Now, a seven-year investigation has concluded his actions probably resulted in "more lives being lost than saved", with the UK government being urged to acknowledge that many murders were avoidable and to apologise to bereaved families.
On the Sky News Daily, Niall Paterson examines what we know about the British mole and gets reaction to the Operation Kenova report with our senior Ireland correspondent David Blevins.
Podcast producer: Sydney Pead
Interviews producer: Melissa Tutesigensi-Charles
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Editor: Wendy Parker
