FBI search teams have swooped on the secluded farm where alleged killer Cristhian Rivera lived - just minutes after it was revealed Mollie Tibbetts's death was caused by multiple stab wounds.

Three agents with K-9 dog units were seen on Thursday afternoon showing a warrant to the occupants of the ramshackle rural property before heading inside.

DailyMail.com understands the raid is linked to the ongoing search for the weapon that caused the 'multiple sharp force injuries' to 20-year-old Mollie's body.

It was the first time the FBI had visited the house since Monday afternoon, when an agent was seen accompanying local law enforcement when Rivera was taken into custody.

An autopsy conducted on Wednesday revealed Tibbetts was killed by 'multiple sharp force injuries.'

The agents, from the FBI's Omaha, Nebraska, Evidence Response Team, arrived just after it was released by Iowa law enforcement.

K-9 search: FBI agents with dogs were involved in the hunt at the farm on Thursday

Mollie Tibbetts, whose body was found on Tuesday after a month-long search, was killed by 'multiple sharp force injuries,' an autopsy concluded. Cristhian Rivera, 24, has been charged with Mollie's murder after allegedly attacking and abducting her on July 18

Starting searching: K-9 handling agents and members of the FBI Evidence Response Team swooped on the farm where Cristhian Bahena Rivera, 24, a Mexican native and, according to authorities, an illegal immigrant, was living

Forensic involvement: Agents from the FBI's Omaha, Nebraska, field office's Evidence Response Team went to the farm minutes after Mollie Tibbetts was revealed to have suffered multiple stab wounds

Inspection: FBI agents looked around the trailer which murder suspect Cristhian Bahena Rivera shared with Iris Monarrez. She was at school with Mollie Tibbetts and is mother of his child

Search scene: FBI K-9 units arrive at the farm where Millie Tibbetts's alleged murderer lived to start a search for the murder weapon

Trailer home: Cristhian Rivera, 24, lived in the trailer to the left of the main farm before his arrest on suspicion of murdering Mollie Tibbets. He led law enforcement to her body four weeks after she went missing

Dane Lang, co-owner of Yarrabee Farms, confirmed that Rivera had lived in this trailer 'for the past couple of years' while working on their dairy farm. FBI are now searching the property for the murder weapon

There were at least four people inside the farmhouse when the FBI arrived.

They were led outside and spoken with, though two people, a man and a woman, were allowed to leave.

Two unmarked cars arrived on the property shortly afterward to assist with the search.

FBI officers could be seen examining the back of the trailer where Rivera lived.

An agent with the Evidence Response Team was then seen taking photos of the exterior of the farmhouse.

A K-9 agent then took a dog out of a car and headed inside the building, which has a large basement according to property records.

The state medical examiner announced that her death has been ruled a homicide, but no details were released about what caused the sharp force injuries. The agency says further examination may result in additional findings.

The Division of Criminal Investigation released the information Thursday, saying the autopsy also officially confirms that the body found in Iowa corn field on Tuesday was that of missing student.

Cristhian Bahena Rivera, 24, a Mexican native who is suspected of being in the US illegally, has been charged in Tibbetts's slaying.

Investigators say Rivera led police to the body on Tuesday in a cornfield outside of Brooklyn, Iowa.

When police arrested him on Friday, Rivera made a full confession and told them he had seen Mollie before. It remains unclear what his motive for chasing her down and attacking her was.

He told police in his interview that he 'blacked out' and that it was common for him to do so whenever he became upset.

Rivera's chilling confession to police included his description of how he 'came to' after attacking Mollie in the street while he was driving.

Rivera confessed on Tuesday after police found surveillance footage of him following Mollie in his car. He dumped her body in a cornfield and led police to it on Tuesday

Pictured is the dilapidated two-story home - which houses other migrants who work on the dairy farm - and the 30ft long trailer, where Rivera is believed to have lived, is pictured right

The century-old property appears neglected with peeling white walls is surrounded with trash and piles of beer cans

Refuse: Bags of soft drink containers were dumped around the front of the farm

Squalor: This was the scene outside the house where other Mexican workers had been living

Iris Monarrez, (left) Rivera's long-term partner and mother of his daughter, was pictured at his hearing on Wednesday. One of his relatives (right) cried as she watched him be led away by deputies at the end of the hearing

Monarrez (is seen above outside court today) is friends on Facebook with Mollie Tibbetts and her brothers Scott and Jake

According to the friend, the 24-year-old is a 'caring' father. He is pictured with his ex-girlfriend Iris Monarrez, who was friend with Mollie on Facebook, and their young daughter

Rivera's girlfriend Iris Monarrez is seen in a yearbook photos above. She was dating Rivera throughout her years at the school

He then remembered, he said, that she was in his trunk. When he went to retrieve her body, he noticed there was blood on the side of her head.

He then dragged her on foot before putting her over his shoulder before dumping her 20 meters into the cornfield where he hid her corpse beneath corn stalks and leaves.

It is unclear if Rivera knew Mollie personally, but social media reveals his girlfriend, Iris Monarrez was friends with Tibbetts on Facebook and went to high school with her.

For years, his employer said the young man from Mexico presented himself as a legal US resident and reliable worker at Yarrabee Farms, a dairy farm in Brooklyn, Iowa.

Dane Lang, co-owner of Yarrabee Farms, confirmed to DailyMail.com that he had lived in a trailer on the farm 'for the past couple of years.'

Dane's brother is Craig Lang, former president of the Iowa Farm Bureau Federation and a 2018 Republican candidate for state secretary of agriculture.

Monarrez declined to speak to reporters as she left court Tuesday. She is seen above in yearbook photos

Iris Monarrez was on the cheerleading squad and is seen in this yearbook photo circled above

Mollie and Iris actually appear on opposite sides of the same page in the 2015-16 edition of the ‘Make It Count’ yearbook. Mollie is seen circled on the left and Iris right hand page

The prominent Iowa family hires a number of migrant workers and accommodates them in a series of trailers and properties, including a tumbledown dwelling on 200th Street, Brooklyn.

Public records also linked Monarrez to a dilapidated house next to the trailer which sits on 39 acres of farmland and is a six-minute drive from the spot along 385th Avenue where Rivera allegedly dragged Mollie into his car.

But now Rivera is accused of illegally living and working in the US on fraudulent documents.

Rivera appeared in court Wednesday on a first-degree murder charge. He was ordered jailed on a $5 million cash-only bond.

The turn of events stunned the farm family that employed him the last four years. They said even after Tibbetts disappeared on July 18 while out for an evening run in the town of Brooklyn, Iowa, Rivera kept coming to work.

Mollie's grieving family broke their silence on Wednesday during a vigil at the University of Iowa where she would have entered her sophomore year this fall.

Mollie's family says they have forever lost their sense of normalcy since they learned of her death (shown here mother Laura Calderwood center in blue and brother Jake in blue to the left along with other family members on Tuesday during a press conference about her death)

'From our family from our friends from the community of Brooklyn (Iowa), we thank you from the bottom of our heart,'' her brother Jake said.

She was incredible and we're gonna miss her dearly. We're never gonna have that sense of normalcy again.'

Jake also touched upon his sister's legacy, saying 'The stories you've all heard about Mollie over the last month, they're incredible,' he said.

'To be honest, what made her so special was she was just like anyone standing here — she loved to run, she loved Harry Potter, she loved the Hawks, she loved her family, she loved her friends.'

'What made her special is she was so outgoing, so loving, so passionate,' he said.

'She wasn't a silent person in the literal sense in that when she talked, everyone in the room heard her, and also about things she cared about, things she was passionate about. She wouldn't stay silent if she felt something was wrong, and that's what's so great about her.'

Tibbetts' family also issued a statement, saying 'our hearts are broken.'

'We know that many of you will join us as we continue to carry Mollie in our hearts forever.'