ST. PETERSBURG, Fla. -

A Tampa Bay mother was charged with first-degree murder after authorities say she fatally stabbed her 4-year-old son Friday night.

St. Petersburg police said Tasha Trotter was waiting on the apartment's porch when Joseph Artis and his grandmother came home. Police said Trotter was acting odd and grabbed a knife once inside the house and went after the boy. Police said the grandmother, Carolyn Trotter, tried unsuccessfully to stop her.

A short time later, the 40-year-old woman carried her son out the front door. Police found the boy outside with multiple stab wounds. Artis, who lived with his grandmother, was pronounced dead at the hospital.

Neighbor Sherry Ford told the Tampa Bay Times she heard screams from her home.

Officers told Trotter to hand over the child and she complied.

"She just laid him on the ground," Ford said. "She just politely laid him on the ground. She still had the knife in her hand."

St. Petersburg police say Tasha Trotter did not want to talk to detectives Friday night and said they don't have a motive for why she allegedly stabbed her son. She was taken to Pinellas County Jail. It's unclear if she has retained an attorney.

Department of Children and Families officials worried about the boy's safety in 2009 after receiving a call about violence in the home that appeared to involve the child's father. Trotter and the boy moved in with the child's grandmother and the father agreed not to contact the child, DCF spokeswoman Natalie Harrell said.

In 2010, Trotter voluntarily gave the boy's grandmother, Carolyn Trotter, temporary guardianship and moved out of the home. A judge made it permanent a year later.

Two other siblings, one older and one younger, had already been removed from Trotter's custody prior to the stabbing, according to DCF.

DCF officials were unable to provide what treatment, if any, Trotter had received, due to privacy laws. Family members told police she had a history of mental illness and has been in and out of several treatment facilities.

Linda Maibauer lived across from Trotter and told the newspaper she'd heard the woman screaming inside her room or throwing things against the walls in recent weeks. Maibauer said Trotter sat outside on a couch cutting clothes with a kitchen knife and stabbing the knife into the ground.