Jurors have found Waseem Daker of Georgia guilty of killing a flight attendant, Karmen Smith, in 1995 and stabbing her then-5-year-old son Nick 18 times.
Jurors at the trial in Marietta, Ga., started deliberations at 9:21 a.m. and came back with a verdict at about 3 p.m.
Daker was found guilty of felony murder, burglary and aggravated battery and stalking.
Jim Horan, Nick's uncle thanked the jury for "seeing the truth."
"She (Karmen) was taken from us too soon by a savage monster..." said Horan. "We know today is not a great day for our family -- it is just another day without our sister, mom, our daughter Karmen. We miss her every day and are glad that justice has been done."
Prosecutors argued that the crimes were revenge against Smith's roommate, Loretta Spencer Blatz, who helped send Daker to prison for harassing her.
Daker, who acted as his own attorney, had long been a suspect in Smith's murder, but it wasn't until 2009 that, according to authorities, tests showed hairs found on Smith's body matched Daker's DNA.
Daker and prosecutors fought over those DNA tests from the scene of the crime that police say cracked the case and led to his arrest.
In the courtroom, Daker questioned homicide detective John Dawes and asked why police did not submit every piece of evidence for DNA testing.
Dawes explained that once officials had Daker's DNA linking him to the crime scene, there was no need for more tests, to which Daker asked, "Which is more expensive? Doing a DNA test or sending an innocent man to prison?"
During the trial, prosecutors played a 17-year-old recording of a phone call between Blatz and Daker, who Blatz who met while participating in a paintball group when she was 30 and he was 17.
"I don't know why you get so freaked out and you frighten me, and you know you frighten me and I don't appreciate it," Blatz was heard saying on the call.
Daker responded, "Maybe you're scared of me but ... you always think I'm going to kill you. You know you're lying because you know I got better things to worry about than you."
Jurors were presented with 12-year-old emails that prosecutors said proved Daker obtained disturbing materials before the murder. The "how-to" titles were "How to Get Away with Murder," and, "Kill Without Joy."
Blatz and Karmen Smith's son, Nick Smith, now 22, both took the stand during the trial, which made for some awkward questioning as they were grilled by Daker.
Judge Mary Staley nearly lost her cool a few times in this case, clearly annoyed with Daker's courtroom antics.
"There are numerous occasions during the trial that your veracity has been in strong question by me. Strong!" said Staley. She added, "And you don't try cases by ambush."
On Sept. 14, Blatz took the stand and was clearly rattled having to be grilled by the man imprisoned for stalking her and accused of murdering her roommate.
Daker's Sentencing is set for Oct. 1.