An Ecuadoran court has sentenced Luis Guaman to 25 years in prison, the maximum penalty under their criminal code, for the beating deaths of a young mother and her 2-year-old son last year in Brockton.

Luis Guaman

The sentence appeared online late Monday, one week after three judges in the city of Cuenca declared Guaman guilty of murdering housemate Maria Avelina Palaguachi and her son, Brian, in February 2011 and dumping their bodies into a trash bin behind their house. Guaman will get credit for several months served in jail and must pay a fine of $10,000 to the victims’ family members, according to the decision handed down by the Third Criminal Court of Azuay in the city of Cuenca.

The sentence followed a brief and controversial two-day trial in Ecuador held over the vocal objections of Plymouth District Attorney Timothy J. Cruz, who demanded that Ecuador extradite Guaman to Massachusetts based on the existing extradition treaty between the two nations.

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Ecuador refused, saying its constitution bars the extradition of its own citizens, and implored Cruz to help them prosecute Guaman in Ecuador instead. Cruz refused, and called for the United States to impose economic sanctions on the South American nation.

In Massachusetts, Guaman would have faced life in prison without the possibility of parole. In Ecuador, he faced 16 to 25 years in prison.

In a telephone interview today, Maria Eloisa, the older sister of Maria Avelina Palaguachi, said she is worried Guaman won’t serve the full 25 years for killing Palaguachi and her 2-year-old son, Brian, because in Ecuador prisoners can be released before they finish their sentences.

“Twenty five years is not enough for killing two people,” Eloisa said in a telephone interview from her home in Brockton. “God willing, he’ll come back here. He should be tried here. My nephew, Brian, was an American. He was born here and that’s why I want justice here.”

Eloisa said it is a relief to know that at least Guaman will not be on the streets.

“This man is not a Christian. He’s a demon,” she said, speaking in Spanish. “As long as he’s not harming anyone, we’re happy. But we still hope he’ll come back here.”

Cruz, in a telephone interview today, said he would not relent on his demand that Guaman be returned to the Bay State to stand trial. He said that he believes that under Ecuadoran law, Guaman could remain imprisoned for as little as 10 years.

“I have no faith whatsoever in the length of the sentence,’’ Cruz said in a telephone interview. “I have no faith in their trial system over there. I still think Guaman should be extradited and we would deal with him here.’’

Cruz said it is now up to the Massachusetts congressional delegation and the Obama administration to pressure Ecuador into sending Guaman back to Massachusetts. He said that the United States must live up to its treaty obligations with Ecuador and other countries, and should also require Ecuador and other countries to abide by their treaties.

“What if this was to happen to somebody you knew or to your loved one? Are we supposed to forget about it? I am not prepared to do that,’’ Cruz said. “I have an obligation to that little boy and his mother. I am willing to try this case, and to let the chips fall where they may.’’

Guaman, a 42-year-old former roofer, had pleaded innocent and said the pair were alive when he caught a flight to his native Ecuador hours after the bodies were found. He used another man’s passport to get through airport security in New York.

In Ecuador, judicial police quickly arrested him in February 2011 for passport fraud, with help from his estranged wife in New York who told officials he had called from Ecuador and threatened to kill their children and her parents there if she did not send him money.

Ecuadoran officials prosecuted him for passport fraud and he served several months in jail for those charges. Then he was held for several more months pending the murder charges, and the court said he would get credit for time served.

In Massachusetts, Guaman has been indicted on two counts of first-degree murder. Cruz has said he will keep trying to extradite him.

Guaman’s defense attorney, Italo Palacios, has said he would appeal the decision.

Prosecutor Rocio Polo cheered the court’s sentence on Tuesday, even as she prepared for a possible appeal.

“I might have to fight again,” she said. “No problem. We’ll fight to the end.”

John R. Ellement of the Globe Staff contributed to this report.