Cristhian Bahena Rivera testified at his murder trial on Wednesday and is facing one count of first-degree murder in the July 2018 stabbing death of Ms Tibbetts.
Ms Tibbetts was 20 years old at the time of her death.
If convicted, Mr Rivera will face a mandatory sentence of life in prison without parole.
Mr Rivera claimed that the unidentified men killed Ms Tibbets and left him with the body.
He claimed he dumped the woman's body in a cornfield and did not report the incident because he was afraid law enforcement would learn he was in the country illegally and would deport him.
According to his testimony, he exited his shower on the day of the murder and found two men waiting for him in his living room wearing dark sweaters and face coverings.
He said there was a larger man holding a gun and a smaller one holding a knife.
According to Mr Rivera, the men told him he “shouldn't do anything stupid and everything was going to be okay”.
He said that the men never directly threatened him, but directed him to get into his car and to drive directly to Brooklyn, Iowa, where they came across Ms Tibbetts.
The men allegedly instructed him to drive past Ms Tibbetts several times while they ducked down low in the car.
At one point Mr Rivera claimed the men told him to stop the car, and the man with the knife exited and began walking down the road towards town, the same direction Ms Tibbetts was traveling.
He said the man was gone for 10 to 12 minutes while he and the larger man waited in the car. He said he heard the man in the car whisper "Come on Jack," apparently referencing Dalton Jack, Ms Tibbetts' boyfriend.
During Mr Jack's testimony, he was confronted with phone records showing he only called Ms Tibbetts once in the days after her disappearance. He was also confronted with Snapchat messages showing he had been cheating on Ms Tibbetts with another woman, and asked about his temper.
Police said they do not consider Mr Jack a suspect because they confirmed he was out of town on work when Ms Tibbetts went missing.
Once the smaller man returned to the car, the group allegedly continued driving for some distance before the men got out and told Mr Rivera to keep driving.
During the transition he claimed he heard the men put something in the trunk. They got back in the car and allegedly told him to keep driving down a gravel road until they approached a corn field.
The men said they knew about Mr Rivera's ex-girlfriend and daughter, and told him that if he said anything about the events he witnessed they would “take care of them”.
Before the men left Mr Rivera, they took his cellphone and his keys. He decided then to check the trunk, where he found Ms Ribbett's body alongside his cellphone and keys.
An autopsy found that Ms Tibbetts had been stabbed seven to 10 times in the chest, ribs, neck and skull.
Her body was badly decomposed and hidden beneath corn stalks when it was found.
He claimed he debated what to do for several minutes before deciding to dump her body in the cornfield and covering her up because he “didn't want her to be exposed to the sun”.
Ms Tibbetts was fully dressed at the time of her death, save for one shoe.
Mr Rivera claimed he did not call the police because he “was scared”.
Jennifer Frese, Mr Rivera's defence attorney, claimed that police “coerced a confession out of him” after a 12 hour work day.
She also claimed that police closed the case too early and did not conduct a complete investigation of Ms Tibbetts' murder.