The soldier was upset that he was granted only a 24-hour leave to attend her funeral, which was delayed for nearly a week so he could be there, the spokesman said. The leave was then extended to two days.
Lopez joined the island's National Guard in 1999, and he served on a yearlong peacekeeping mission in Egypt's Sinai Peninsula in the mid-2000s. He enlisted with the Army in 2008, and arrived at Fort Hood in February from Fort Bliss, a Texas post near the Mexico border.
He saw a psychiatrist last month and showed no "sign of any likely violence either to himself or others," McHugh said.
Suzie Miller, a 71-year-old retired property manager who lived in the same Killeen apartment complex as Lopez, said few people knew him and his wife well because they had just moved in a few weeks ago.
"I'd see him in his uniform heading out to the car every morning," Miller said. "He was friendly to me and a lot of us around here."
Associated Press writers Ramit Plushnick-Masti in Houston; Christopher Sherman in McAllen; Robert Burns, Eric Tucker and Alicia Caldwell in Washington; and Dánica Coto in Guayanilla, Puerto Rico, contributed to this report.