Jesse Dobbs, 23, was sentenced to 45 years in prison along with a $10,000 fine.
Dobbs reportedly stabbed Kirsten Fritch nearly 60 times, dumping her body in Texas City. He was arrested in a bar nearby, where he walked in barefoot and asked for a glass of water.
In charging documents, Dobbs told detectives that he killed the "fake" Kirsten.
"Kirsten is dead, I killed her -- not the real Kirsten but the fake Kirsten," the document stated.
Kirsten's mother, Cynthia Morris, was murdered days before Kirsten's body was discovered by searchers.
Morris and her 13-year-old daughter, Breanna, were found shot to death in their Baytown home. Baytown police say they are still investigating these murders, and consider Dobbs the main suspect.
VIDEO: Police detain 'person of interest' in Baytown Amber Alert case
"Obviously he is really our only suspect in that case and that's not really based off of some preconceived notion, it's based on all of the evidence we've gathered," said Lieutenant Steve Dorris of the Baytown Police Department.
According to Lt. Dorris, there is no statute of limitations for either case and the department is taking their time to carefully collect evidence to ensure they can get a conviction.
Kirsten's grandmother said she had met Dobbs online just a couple of weeks before her murder.
Dobbs has two children from a previous relationship. He was charged with domestic violence against the children's mother, who said he was known to use methamphetamine.