A father's domestic violence rampage at a Milwaukee duplex on Friday morning critically injured two people and left two others dead, including his 5-month-old daughter who was fatally stabbed in her crib.

The baby's 19-year-old mother and her new boyfriend, 22, were rushed to a Milwaukee area hospital where the woman underwent surgery, according to Milwaukee Police Chief Edward Flynn. The suspect, believed to be the mother's ex-boyfriend, has been arrested after being found in a bathroom at the residence with superficial stab wounds.

"The offender, the man we've arrested, is apparently the ex-boyfriend (of the mother) and father of the dead baby," the chief said. "The young man who was stabbed is someone who very recently established a relationship with the mother of the baby. Obviously the mother of the baby has been seriously wounded. Also murdered was an older man in the apartment who was basically a friend of the family."

At about 8:30 a.m. on Friday, the infant's mother contacted police authorities while she was being attacked inside her house. Upon reaching the crime scene, police found four stabbing victims after having forced their way into the house, the Journal Sentinel reported.

While both the infant and a 39-year-old man, described as a family friend, were found dead, the mother and her alleged boyfriend were seriously wounded, Flynn said, adding that even though the suspect has provided some information, investigators are still attempting to confirm the relationships between the victims and the suspect.

However it was confirmed by authorities that prior incidents of domestic violence had taken place, but none of them had been reported to the police.

"We have learned from the people at the scene that there previous incidents of domestic violence, but none have ever been reported to us," he said, adding that the parents had a troubled relationship.

"We've had an impact periodically on domestic violence when we can get chronic offenders and chronic victims help," Flynn said. "This one's not on our radar screen and it is those that tend to be the most volatile because we don't know what we don't know."

"When one of these erupts into deadly violence, the results are tragic," he added.

Meanwhile, Mayor Tom Barrett and Common Council President Michael Murphy, who represent the area where the stabbing occurred, urged people who witness domestic violence to report it, according to the Associated Press.

"My message to people in relationships or who have ended relationships, is if you suspect something, you should seek out help," Barrett said.

On Friday morning, the infant's mother still remained in surgery.

"If she recovers, I cannot imagine the nightmare that she faces," Murphy said. "... We need more compassion in our city, less hatred."