Becky Watts stepbrother and girlfriend guilty of killing

Becky Watts was killed in her home in February. Photo / Facebook

The stepbrother of Becky Watts's has been found guilty of murdering her during a sexually motivated kidnap plot.

Matthews, 28, went to the 16-year-old's home in February, suffocated her in her bedroom and stabbed her in the abdomen 15 times after her death.

He then dragged her body into the boot of his car and drove it to the home he shared with his girlfriend.

Matthews then bought a saw, goggles, masks, bags, cling film and tape to cut up and package Becky's body.

His girlfriend Shauna Hoare has been cleared of the murder but found guilty of manslaughter.

Nathan Matthews and Shauna Hoare Photo / Police

The pair were convicted of conspiracy to kidnap Becky, perverting the course of justice and preventing a lawful burial. Two other men, James Ireland and Donovan Demetrius were acquitted of assisting an offender.

Detectives who investigated the case said the couple had a "sinister" motive for killing the Watts, for whom they had developed hatred for, the Daily Mail reported.

Speaking after the verdict, the family of Becky Watts paid tribute to her, saying: "We loved Becky and knew her better than most," the Daily Mail reported.

"We can tell you that she was a beautiful, happy, funny, feisty, caring, loyal and witty girl. She was like a tornado, hurricane and sunbeam all at once. She came into your life and made you feel alive."