A note from Expugnatio Hibernica, it reads: For de Lacy's fall from royal favour, see Orpen, Normans, ii. 54-5. His marriage in 1180 to the daughter of King Ruaidri Ua Conchobair of Connacht may have given colour to the suspicion that he was aiming at his own independent kingdom in Ireland.
When Prince John returned to England in 1185. after his disastrous visit to lreland, he
reported to King Henry that de Lacy had prevented the Irish kings from sending him
(John) either tribute or hostages, see A.F.M., under 1185. William of Newburgh
Hist. rer. Anglic., i, 239-40, mentions the story that de Lacy was aspiring to rule Ireland treated Henry's messengers in high-handed fashion, and that the aews of his murder was joyfully received by Henry in 118
Surely a fella of Henry's disposition made sure to have some solid local contacts. I'm intrigued by this note in FX Martin's version of Expugnatio.
Means, motive and opportunity?