 CONT: The movie implies that the contamination of Raccoon city was  caused by the scientists reopening the Hive. During the first movie,  while under the train reconnecting the power cable, Rain sees clear  evidence that something has escaped through a grate. The hole in the  screen matches the holes in the dog cages seen later in the movie,  implying that one or more dogs, or other infected animals have  already escaped into the city.