Authorities have announced a first-degree murder charge against Christian Rivera, 24, in the death of Iowa college student Mollie Tibbets.

Rivera is an undocumented immigrant and led detectives to her body in rural Poweshiek County, according to Iowa investigators.

The charge was filed more than month after Tibbetts went out for a jog and disappeared - and days after investigators searching for the missing Iowa college student said they were focusing their efforts on five locations.

For 34 days, federal, state and local authorities had scoured Poweshiek County for Tibbetts, and sifted through electronic data from her Fitbit, cellphone and social media accounts for any clue about what happened to the woman who was last seen alive while going for an evening run. They'd also interviewed nearly 1,500 people.

Authorities, who had narrowed their search to a carwash, Tibbetts's boyfriend's home, a truck stop and two farms.

The University of Iowa student's last known communication was a July 18 Snapchat message she sent to her boyfriend, Dalton Jack, for whom she was house sitting, according to the Register. Jack, who was out of town, looked at it but didn't immediately reply.

His "good morning" text the next day received no answer, and Tibbetts didn't pick up her phone when someone at the day-care center where she worked called to ask why she didn't show up. Every call went straight to voicemail.

Assistant Director of DCI Field Operations Mitchell Mortvedt told NBC affiliate WHO-DT that Tibbetts's family members and her boyfriend have been cleared of suspicion.

Her family and dozens of volunteers in the small town of Brooklyn, population nearly 1,500, have been combing ditches, cornfields and empty buildings for any sign of Tibbetts. CBS News affiliate KCCI reported that authorities have also searched pig farms in the area, and last week authorities announced they were narrowing the search.

"It's frustrating. It's powerless. We're racking our brains, thinking what can we think of to tell the investigators," Kim Calderwood, Tibbetts's aunt, told the Des Moines Register. "It's the worst thing - to want to fix something you can't fix."

Mollie's brother, Jake Tibbetts, told the newspaper the family went "through stages of scared and sad. And now we're anxious and confused."

"Mollie has the biggest heart of anyone we ever knew," he said. "She was never shy. . . . She had room in her heart for everyone."

Tibbetts was born in San Francisco and moved to Brooklyn with her mother when she was in second grade. She won state speech competitions, was involved in theater and ran cross-country. She was studying psychology, as her mother did.

As people searched, those closest to Tibbetts asked everyone to hold on to hope - and keep sharing information about her.

"We remain in awe and indebted to the help, creativity, outreach and love that you have shown Mollie and all of us," Sandi Tibbetts Murphy, a cousin, wrote on the wall of the Finding Mollie Tibbetts Facebook page. "Please keep sharing Mollie's information so we can bring our girl safely home."

Greg Willey, of Crime Stoppers of Central Iowa, told the AP that $400,000 raised for information leading to Tibbetts' safe return will instead go to the person who helps police catch anyone responsible for her death.

"Once they catch their breath, this will turn into a weapon going the other direction to catch the person who did it," he said.