UNIVERSITY PARK, LOS ANGELES (KABC) -- Police arrested a mother on suspicion of stabbing her infant daughter, leaving the child in critical condition Tuesday afternoon in University Park.Authorities said the incident happened around 3:30 p.m. in the 2100 block of Park Grove Avenue. The father found his daughter and called 911 after the attack, police said.The parents of the 6-month-old girl were arguing, police said, and that it escalated when the baby's mother stabbed her own child with a pair of scissors. The mom was identified as Maria Mendez."The mother attacked the baby in front of the dad. We can't imagine why a mother, who is supposed to be caring for her child, could do such a heinous act," LAPD Detective Moses Castillo said.A woman said she's known the 39-year-old mother since they were young. The friend said the baby was born premature."She was excited when I spoke to her last. I would say it was in December. She was happy to bring the baby home. I didn't see nothing out of the ordinary. She was just excited because this was her first baby," Veronica Roman said.Another witness said the child's parents aren't married, but lived in the residence where the crime took place for years. A neighbor said the home is Mendez's parents and that she lost both of them years ago.The neighbor also said that Mendez's older brother, who is her only living sibling, lives at the home, too.Mendez was arrested on suspicion of attempted murder and is being held on $1 million bail at Los Angeles County Jail.