Police still do not know the cause of death of a man who was found unconscious in the Financial District early Saturday and later pronounced dead, according to the Boston Police Department. “Circumstances surrounding the victim’s death remain under investigation,” said spokesman James Kenneally. “Cause and manner of death are yet to be determined.” Sunday afternoon, police said that the man may have been involved in a physical altercation. The man, in his 20s, has not been named by police. He was found at about 2:15 a.m. in the area of Franklin and Broad streets and was taken to Massachusetts General Hospital, where he died. He appeared to have a head injury, Boston police spokeswoman Cheryl Fiandaca said Saturday night.