Mississippi - 15-year-old Carly Gregg allegedly shot her mother with a revolver and tried to kill her stepfather, charges for which she now been sentenced.

Carly Gregg (then 14) allegedly shot her 40-year-old mother Ashley Smylie with a revolver in March of this year.

Video footage shows how the girl calmly strolled into the family home after the horrific act, her two dogs prancing around her legs as she sat down on a chair in the kitchen.

According to a report by TMZ, Carly is said to have sent her stepfather a message on her dead mother's cell phone immediately after the murder to lure him home.

"When will you be home honey?" she wrote.

After the text message was sent, the teenager hummed a little song.

Later they would both fight over the revolver and stepdad Heath would be wounded in the shoulder.

Further footage, which was also presented in court, shows the moment the girl is arrested by police officers.

The trial in Rankin County, Mississippi attracted attention all over the country this week.

Carly (now 15) also shocked everyone in the courtroom when she couldn't hold back a giggle on one day of the trial.

Her defense lawyers had tried to get Carly out of prison by pleading insanity.

The week-long trial came to an end on Friday and when the verdict was read out, the girl was no longer in a laughing mood.

Carly burst into tears and looked around in despair after learning that she would have to spend the rest of her life behind bars.

The jury found the 15-year-old guilty of first-degree murder, attempted murder, and tampering with evidence.

The girl is said to have rejected a deal with the public prosecutor's office. Had she agreed, she would have been free after 40 years in prison.