There's a slight problem with a murder charge here against the unborn.
If he didn't know the girl was pregnant, it would be impossible to know that she was.
Therefore, if he killed her, not knowing she was pregnant, he could possibly only be charged with the manslaughter of the fetus.
There probably would be no proof whether she told him or not, unless he says he killed her because she was pregnant. But, according to the article, she may not have even known she was pregnant yet, and the age of the fetus is unknown.
Still, (from the article):
An April 5 California Supreme Court case said that a killer does not have to know a fetus existed to be prosecuted for its murder.