The confessions of William Sullivan Jr., 18, and Nicole Kasinskas, 16, detail how the pair botched three attempts to murder her mother Jeanne Dominico.
The teens, who met on the Internet several months ago, told police they planned to kill the woman because she didn't approve of their relationship, the Boston Herald said.
Kasinskas told police they planned to kill her mother by burning down the house but when they tried to light Dominico's bed on fire, they discovered the mattress was fireproof.
The pair then tried poisoning the woman's milk with drugs.
Kasinskas said they then planned to blow up the house, which also failed.
Finally, as Kasinskas stood watch at a nearby convenience store, Sullivan hit Dominico with a bat before stabbing her repeatedly in the throat.
Biologists detail four new deep-sea 'killer sponges'
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend