Story highlights Jerome Lynch is accused of throwing acid in his daughter's face

She reportedly suffered burns over 50% of her body

A motive for the attack is unknown, says the man's niece

A New York man was arrested after police say he poured acid on his daughter, burning her skin and sending her to the hospital in critical condition.

As one of the primary caretakers of Jerome Lynch, 69, Darlene Lynch, 49, was checking on her father in his Brooklyn apartment early Saturday afternoon, when seemingly out of nowhere, the elder Lynch came up behind her and poured acid on her face and down her body, according to Dominique Goodwin, the man's niece.

"Our family just doesn't understand," Goodwin said. "He's not incompetent. He's totally aware of what he did. We just don't know why."

Goodwin said Jerome Lynch had suffered a stroke several years ago, leading to a slur in his speech and a need for a cane or walker to get around.

Goodwin added that her family has no idea where he got the acid.

Police believe the corrosive substance was actually a cleaning solution that contained 98% sulfuric acid.

According to Goodwin, Darlene Lynch suffered burns over 50% of her body -- on her face and over her left side. At one point, it was feared she might lose her left eye, but Goodwin says her cousin is now able to see out of it.

An emergency medical team took the daughter to NewYork-Presbyterian Hospital in critical condition after the attack.

NYPD spokesman Sgt. John Buthorn said Sunday that Jerome Lynch had been arrested and charged with felony assault. Information about his arraignment and legal representation were not immediately available.