A teenager accused of killing a mother and maiming her daughter with a machete during a home invasion was found guilty Tuesday of murder and other charges and was sentenced to life in prison.

The first-degree murder conviction carries an automatic sentence of life without parole. The judge tacked on 76 years to 19-year-old Steven Spader's sentence for his other felony convictions, saying she could go on for days about the depths of his depravity.

The sentence ensures "you will stay in that cage for the rest of your pointless life," Judge Gillian Abramson told Spader.

Spader was the first person to go on trial in the October 2009 attacks that left Kimberly Cates dead and her 11-year-old daughter, Jaimie, gravely wounded. Three co-defendants accepted a plea deal and testified against Spader; a fourth awaits trial.

Jurors deliberated for about 90 minutes before returning their verdicts. Spader, of Brookline, whose birthday is Tuesday, showed no reaction. He was overheard saying to his lawyers before court proceedings began, "Maybe the jury will sing 'Happy Birthday' to me."

As the jurors were being polled individually on each of their six guilty verdicts, several glared at Spader. Six of the 12 reached after the trial declined to comment.

Before Abramson sentenced Spader, David Cates told her about the suffering and shattered dreams the attacks on his wife and daughter caused. He told Spader that no prison sentence was long enough.

"To the murderer in this courtroom, the upcoming sentence is not justice," Cates said. "My only hope is that very soon, true justice finds you."

The jury found Spader guilty of both premeditated murder and intentional murder during the commission of a burglary. It also found him guilty of attempted murder, conspiracy to commit both murder and burglary, and tampering with a witness.

His mother, Christine Spader, wept briefly as the verdicts were read; his father was stoic.

Defense lawyers Jonathan Cohen and Andrew Winters said they were disappointed by the verdicts but refused to answer questions.

Prosecutor Jeffery Strelzin said after the 11-day trial that the "sheer randomness" of the crime may have been its most horrible element.

Spader wielded a machete and co-defendant Christopher Gribble used a knife during the attacks in the Cates' Mont Vernon home, authorities said. Jaimie, now 12, survived by pretending to be dead, then staggered, covered in blood, to a kitchen phone to call police. A doctor testified she would have died of a punctured lung if she had lost consciousness before summoning help.

Blows that cut off portions of Jaimie's left foot, split open her head and struck her face with enough force to break her jaw had to have come from a heavy and sharp weapon such as a machete, several doctors testified.

David Cates told the court that Jaimie gets A's in school and played on the field hockey team this fall. But he said her emotional scars are immeasurable.

"She has had to witness more evil in this world than any human being should be made to bear," Cates said.

Cates described his late wife as his soulmate.

"Kim was full of energy, excitement and love," said Cates, who was traveling on business when the attacks occurred.

In their final arguments, Spader's lawyers assailed the character and credibility of the three co-defendants who testified against Spader. Even Strelzin described them as despicable.

But the strongest evidence against Spader were his own words — his bragging to friends about the attacks and detailed notes he wrote to his cellmates while awaiting trial.

Spader wrote that he whacked the mother 36 times and could see brains, lots of blood and her eyeball hanging out of its socket.

"I am probably the most sick and twisted person you will ever meet," Spader wrote as the prelude to one of his notes to a fellow inmate.

One of Spader's co-defendants pleaded guilty to conspiracy to commit murder and burglary and accomplice to first-degree assault in exchange for a 30- to 60-year prison sentence. Another pleaded guilty to robbery, burglary and conspiracy in exchange for a 20- to 40-year sentence.

And a third co-defendant who testified against Spader but was not present during the attacks faces five years in prison for hindering the prosecution.

Gribble, the fourth co-defendant, is scheduled to go on trial in February.