Irish Catholic rebels, likely under the command of Toole McCann, killed about 100 Protestant settlers by forcing them off the bridge into the River Bann and shooting those who tried to swim to safety.

It began as an attempted coup d'état by Catholic gentry and military officers, who tried to seize control of the English administration in Ireland.

They wanted to force King Charles I to negotiate an end to anti-Catholic discrimination, and greater Irish self-governance, and to partially or fully reverse the plantations of Ireland.

Canny writes, "the bloody mindedness of the settlers in taking revenge when they gained the upper hand in battle seems to have made such a deep impression on the insurgents that, as one deponent put it, 'the slaughter of the English' could be dated from this encounter".

[5] It is likely that the prisoners were being brought to the coast to be deported to Britain, and rebel leader Felim O'Neill had already sent other such convoys safely to Carrickfergus and Newry.

[5] Toole McCann was the rebel captain in charge of the Portadown area at the time, and several people made statements that he was responsible for the massacre.

[8] In County Tyrone, modern research has identified three blackspots for the killing of settlers, with the worst being near Kinard, "where most of the British families planted ... were ultimately murdered".

[11] Though a supporter of British rule in Ireland, 19th-century historian William Lecky wrote "it is far from clear on which side the balance of cruelty rests".

Protestant bishop Henry Jones led the inquiry and read out some of the evidence to the English parliament in March 1642, although most of his speech was based on hearsay.

Massacres were committed by Oliver Cromwell's army during this conquest, and it resulted in the confiscation of most Catholic-owned land and mass deportations.

One woman stated that Irish Confederate commander Owen Roe O'Neill went to the site of the massacre when he returned to Ireland in 1642.