A man has been sentenced to life in prison for attempted murder and conspiracy to commit murder in a plot to kill his teenage girlfriend's siblings and her parents in suburban Detroit.

The Detroit Free Press reports that 24-year-old Michael Rivera made a brief statement Thursday in Wayne County Circuit Court, saying: "I'm sorry for my family, for them having to go through this."

Prosecutors say the then-15-year-old girl stabbed her 12-year-old brother in the neck and tried to stab her younger sister Oct. 17 in their Plymouth Township home. Police say Rivera guided the girl from outside the house, advising her on what knife to use.

The girl was charged as an adult in the case. The Associated Press isn't naming the girl or her family members.