A high school teacher's Christmas card to a colleague cost him his life after a jealous husband found the 2-year-old card in his home and incorrectly decided his wife was cheating on him, authorities said Friday.

Jerry Metaxas gunned down John Sacci in front of his school and dozens of students and friends, then killed himself on Thursday, a year after he found the discarded holiday card addressed to his wife, Linda, authorities said.