The father and the mother were obviously no longer together, since the mother' boyfriend was also wounded. Whether the UNNAMED DAD had legal custody/visitation is not explained, nor why he had access.
http://www.duluthnewstribune.com/news/crime/3662884-wisconsin-father-accused-stabbing-infant-daughter-death
Wisconsin father accused of stabbing infant daughter to death
By Mark Guarino, Reuters Today at 3:46 p.m.
A Wisconsin man is suspected of stabbing his 5-month-old daughter to death in her crib on Friday and killing a family friend in a violent attack in which two other people were wounded, including the child's mother, Milwaukee police said.
The baby's 19-year-old mother and her 22-year-old boyfriend, who is not the child's father, suffered stab wounds and are being treated in a local hospital, while a 39-year-old family friend was stabbed to death, according to police.
Police said they arrested a man who they found in a bathroom of the Milwaukee apartment where the attack occurred suffering from superficial stab wounds. He is identified as the father of the child.
"We are not seeking any other suspects," Milwaukee Police Chief Ed Flynn told reporters, adding that the investigation was ongoing and that the wounded couple had "recently established a relationship."
Police did not identify the suspect.
Flynn said homicides have spiked in Milwaukee so far this year, with 13 homicides recorded in January compared to just one by this time a year ago.
A call and email to a Milwaukee Police spokesman was not immediately returned.