 There is little documentation of the decision to taken by the Provisional government, headed by Collins, to attack the Four Courts; Historian Michael Hopkinson writes, 'the scarcity of evidence is explained by the acute sensitivity of the subject, both at the time and since'.When Collins arrived back in Dublin, his forces began to act against the anti-Treatyites.On June 27 they arrested anti-Treaty IRA officer Leo Henderson as he was enforcing the Belfast Boycott by seizing cars.