Thanks to advancements in DNA testing, FDNY Lt. Jeffrey Walz, who died in the World Trade Center’s north tower at age 37, was recently identified from a bone fragment found in a boot recovered shortly after the 9/11 attacks. Walz’s family, including his widow and now 15-year-old son, got the news on Friday. “It’s a little bit of a shock, but it was something that I felt would come about,’’ said Walz’s sister, Karen Ciacco. “We always felt that we would get something from him. I felt as though he came home to the family.” According to the city’s Medical Examiner’s Office, only 1,637 of the 2,753 WTC victims have been identified.