BBC的新闻里有个句子不懂.
The incident began on Thursday morning when the gunman killed four workers at a busy supermarket in Espoo. Later, the police found the 5th body in a flat nearby. It was that of the killer's estranged partner. She also worked at the supermarket, and the police have described her as the main target, and there are indications that the other victims were killed because of their links with her. The gunman's body was later found in another flat. He was named as 43-year-old Ibrahim Shkupolli, a Kosovo-Albanian who had lived in Finland for several years.
就是这句话It was that of the killer's estranged partner. 是什么句型啊?