A man once charged with two counts of first-degree murder for killing a Salt Lake father and his son pleaded guilty Friday to reduced charges of aggravated assault.

Richard Gabaldon, 20, Salt Lake City, pleaded guilty to two counts of aggravated assault, a third-degree felony, before 3rd District Judge Richard Moffat on Friday as part of a plea bargain with the Salt Lake County attorney's office. He was allowed to plead to the reduced charges in exchange for his testimony against his friend, Fred A. Alvarez.Alvarez was convicted in November of stabbing Don Newingham, 39, to death during a fight in June 1990 and was sentenced to serve the rest of his life in prison. He was acquitted of killing Newingham's 18-year-old son, Shane, who also was stabbed to death during the fight.

The judge also tacked on an additional 20 years to his sentence because of a new state statute aimed at punishing gang members.

In pleading guilty to the reduced charges, Gabaldon admitted assaulting the Newinghams by use of force during a fight that began after Donald Newingham was denied entry to a party at Gabaldon's Rose Park home on June 9.

"Mr. Gabaldon kicked both individuals while they were down on the ground and unable to defend themselves," said his defense attorney, Andrew Valdez.

Gabaldon will be sentenced on March 21. Each third-degree felony carries a maximum penalty of zero to five years in prison and a fine of up to $5,000. But prosecutors also will ask the judge to add three years to the sentence for each of the charges under the gang-enhancement statute.

Deputy Salt Lake County Attorney Kent Morgan said he will rely on the defendant's own statements made during the trial to convince the judge the crime took place "in concert with two or more persons," as the gang statute states. But Valdez said he will present evidence that his client should not be given the additional prison sentence.

"We intend to challenge the constitutionality of the enhancement itself," he told the judge.