There is no doubt that 15-year-old Tiffany Gayle's beating death was at the hands of both of her parents, the Crown argued Thursday, calling it a vicious "team" act in closing statements at their first-degree murder trial.

"Each of them is responsible legally for what the other is doing," Crown attorney Brian McGuire told a jury, referring to the Brampton teen's father and stepmother, Federick and Elizabeth Gayle.

"They're acting as a team," McGuire said.

It's alleged that both parents — one wielding a baseball bat; the other a barbecue utensil — inflicted the fatal blows that ended the Tiffany's life in the bloody basement of their family home in June 2010.

The beating allegedly started in the garage, then moved to the basement foyer, and finally ended in a bathtub, court heard. The tub was smeared with blood and also had dents in it.

"How hard that person was swinging boggles the mind," McGuire told the jury.

Teen had broken rule about phone calls

Tiffany's five-foot-four, 115-pound body was discovered in that tub. It's alleged the parents tried to cover up the crime, cleaning up blood on the floor, though spatter was found on their clothing. Their bloodied footprints were also found at the scene.

As for why parents would to this to their child, the Crown said a clear motive may be missing, but that evidence presented shows the teen was in conflict with her guardians.

In notes, she wrote she didn't want to be in this world anymore because she felt she caused her family too much pain.

"I hate to see my parents angry, but I guess there is nothing I can do," she wrote.

Her half-sister, Samantha, testified last week that the accused had been planning to send Tiffany back home to Jamaica, where she had moved from a little more than a year before her murder.

The accused had discovered that Tiffany had broken an apparent house rule about making phone calls, the Crown said, telling the jury that she had borrowed a friend's cellphone to contact her biological mother.

Pathologists ruled Tiffany's cause of death to be blunt-force trauma and determined that she died of shock after massive blood loss and internal bleeding.