Weber County Attorney Dee Smith said it wasn't yet clear what charges Stewart might face once the shooting investigation concludes.
"But it appears right now, with the information we have, that we have an aggravated murder as well as a number of other attempted aggravated murders," Smith said, choking back tears.
Aggravated murder is a capital crime and, if convicted, Stewart could face the death penalty.
The officer killed, Jared Francom, was with the Ogden police. He leaves behind two daughters, aged 3 and 5, and his wife of seven years, Erin.
"She's upset, but she's hanging in there," Frisby said of his daughter. "I can only describe her as a rock."
Joining the narcotics strike force had long been Francom's dream job, according to his father-in-law, John Frisby. Francom, 30, had worked as a part-time patrol officer and took security jobs on the side until he was finally chosen for the select group.
It was a "big honor," Frisby said when reached by telephone at his home in Henderson, Nev. "He was good at it."
By mid-day Thursday, more than 1,000 friends and strangers had expressed their support and gratitude for Francom and his family on a memorial Facebook page with prayers, poems and other message. Some posters swapped out their profile pictures for a black logo with a blue stripe representing fallen officers.
Authorities said the conditions of the officers ranged from serious to critical. They are Ogden officers Shawn Grogan, Kasey Burrell and Michael Rounkles, Weber County sheriff's Sgt. Nate Hutchinson and Roy officer Jason VanderWarf.
Kevin Burrell, Kasey Burrell's father, said his son was shot in the head. A seven-year veteran of the police force, the younger Burrell was sedated, but appears to be improving, his father said.
On Wednesday, witnesses said they heard three quick pops followed by a two- to three-minute pause, then lots of gunfire and officers yelling at someone to "put your hands up," in the backyard.
Outside Stewart's house on Thursday armed SWAT officers clothed in camouflage remained on guard as police continued their search of the property. The yard was taped off and dotted with numbered evidence markers.
Residents said they were shocked to hear there was any drug activity in the area or a shootout on their street.
"This has always been a quiet neighborhood. We've been here for 11 years," said Andrew Mair, who said his wife hid in the couple's basement in fear when the gunfire rang out. "I've never heard anything crazy going on."
Associated Press writer Jennifer Dobner in Salt Lake City and Michelle Rindels in Las Vegas contributed to this report.
- Over 100 missing, 14 dead as strong quake...
- Rubio faces barrage of attacks in Republican...
- 5 things to know about the Super Bowl and sex...
- Search for possible survivors of midair crash...
- Pope's sex abuse panel tells survivor to take...
- Police think 6 Chicago deaths result of...
- N. Korea praises launch, others see as covert...
- Lindsey Vonn wins women's World Cup downhill
- US adds just 151k jobs in January; 4.9... 28
- Obama pushes for every child to learn... 21
- Cruz, Rubio eye NH momentum as Dems... 15
- Donald Trump calls for Iowa election... 14
- Kentucky Sen. Rand Paul quits 2016 GOP... 12
- Once a bromance, now a brawl: Trump and... 10
- 5 things to know about the Super Bowl... 9
- In a U.S. divided on gun control,... 8