A Superior Court judge last week denied a new trial to a Guilford man serving two life sentences for the 1999 execution-style slayings of his ex-girlfriend and the toddler she was babysitting. Jeffrey Cookson, 55, of Guilford was convicted by a jury in December 2001 in Penobscot County Superior Court of murdering Mindy Gould, 20, and 21-month-old Treven Cunningham, both of Dexter.