Sao Paulo: The father and stepmother of a five-year-old girl apparently thrown from a sixth-floor apartment turned themselves in to police on Thursday but denied any involvement in her death.

Alexandre Nardoni, 29, and his wife, Anna Carolina Jatoba, voluntarily went to police after a judge issued a warrant for their detention, police inspector Aldo Galeano said. The warrant allows the two to be held for up to 30 days while police investigate.

Earlier Thursday, Nardoni and Jatoba wrote separate letters denying their involvement in Sunday's death of Isabella de Oliveira Nardoni.

"I hope someday I'll be heard as a father who grieves the loss of his daughter, not as a monster, which I'm not," Nardoni wrote in his letter, which was posted on the Web sites of major newspapers and read on news broadcasts. "We are not guilty. Those guilty will be found," the letter said.

Police believe Isabella was thrown from her father's apartment but are not sure whether she was killed before or after the fall. Preliminary tests on her neck and lungs indicate she may have been strangled, and only her wrists were broken.

Blood in the room

Authorities are treating the death as a homicide because there was blood in Isabella's room and a hole in her window's safety netting.

Nardoni has claimed an intruder killed his daughter. He told police he left his daughter on her bed while he went down to the building's parking lot to help his wife and other two children. He said he locked the apartment's door, but Isabella was gone when he returned.

Neighbours told police they heard a girl yelling "Stop, dad!" shortly before she was found on the ground below.