Police identified the fatality as Roel Mendoza, of 2129 Makata street, Sta. Cruz. His body was retrieved by Philippine Navy frogmen under the concrete flooring of the Boardwalk.
His daughter Jen Mariel survived and is now recuperating at the Manila Doctors Hospital.
Police arrested Jemilyn Tuazon, 23, married, of 398 Dayao street in Balut, Tondo, after shocked promenaders at the Rizal Park witnessed how the suspect tried to drown the young girl.
SPO2 Edgardo Ko said Mendoza spent the evening at the Boardwalk with his wife Cecille, Jen Mariel and son Jan Gabriel, 4, to celebrate the mothers birthday.
After a leisurely walk at about 11:45 p.m., the family decided to sit on the concrete seawall of Manila Bay to rest and relax.
It was at this juncture when the suspect joined them and uttered, "Ang sarap matulog dito ano (Its nice to sleep here)?"
The wife told investigators they ignored the woman who left after a while. But the suspect returned and suddenly grabbed their daughter and tossed her into water.
The woman also jumped into the water then tried to the drown the girl by pushing her down as she struggled to stay afloat.
After gaining his composure, the shocked father jumped into the water, but he failed to surface.
Protacio Dapiton, a park lifeguard, came to the rescue and grabbed the young girl from the clutches of the suspect. Dapiton told investigators he had to kick the woman to free the child and take her to safety near the seawall.
The woman also headed for the seawall, where policemen were waiting to handcuff her.
Investigators said they could not get a sensible statement from the suspect as the woman kept changing her story.