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A family of four on vacation from southwestern Iowa was found dead in a Mexican resort-town condominium Friday morning, authorities said.

Kevin Wayne Sharp, 41, Amy Marie Sharp, 38, and their children, Sterling Wayne Sharp, 12, and Adrianna Marie Sharp, 7, were found dead by authorities after conducting a welfare check in Tulum, Mexico.

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The State Attorney’s Office of Quintana Roo, a state on the Yucatan Peninsula, confirmed the ministry is investigating the cause of the family's deaths. During the initial inspection, there were no signs of injury or violence to the bodies or in the room, authorities said. Officials said Saturday that the foursome died of gas asphyxiation.

Jana Weland, Amy Sharp's cousin, told ABC News the family went to Mexico to enjoy the beach and meet friends. There were no signs of forced entry into the condo, Weland said in a video posted to Twitter by the Des Moines ABC affiliate.

"They went to sleep and never woke up," she said.

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The U.S. State Department confirmed the bodies of four U.S. citizens were found in Akumal, Mexico, which is near Tulum on the Caribbean coast of the Yucatan Peninsula.

Around midnight Thursday, the Sharps' family members reported their relatives missing to Creston police.

Ashli Peterson, whose relationship to the Sharp family could not be confirmed, posted on Facebook on Thursday night that the family left the United States for Tulum on March 15. They were supposed to return from their trip on Wednesday and arrive in St. Louis. Then, the family was expected to travel to Danville, Illinois, for a Southwestern Community College men's basketball game Thursday, according to the post.

"The situation with the Kevin and Amy Sharp family is weighing heavily on our hearts and minds," said Todd Lorensen, the Southwestern basketball coach. "Members of their families have been strong Southwestern supporters for years. I consider them friends. They were to be here watching us play basketball this week."

Amy Sharp's sister told the Creston News Advertiser that the family flew to Cancun from St. Louis and was renting a car and driving to Tulum, where they were renting a condo.

"On Wednesday at 7 p.m., Amy sent a text to our mom that said, 'We made it to our condo,'" Hoyt told the Creston News Advertiser. "That is the last communication she made."

Creston Police Chief Paul Ver Meer said their investigation determined the Sharp family had not boarded their flight from Cancun, Mexico, to the United States. The U.S. State Department was called along with officials in Mexico. When officials went to the condominium, they found the bodies of the family.

(3 of 3) Police said autopsies are being done in Mexico. Results are pending, but authorities said the family members showed "no sign of any traumatic injury." pic.twitter.com/bYzERgHN7j — KCCI News (@KCCINews) March 23, 2018

There were no visible signs of trauma on any of the family members' bodies, Ver Meer said.

Ver Meer said they are waiting to hear the autopsy results for the cause of death.

It’s unknown when they will be returned to Iowa.

“It’s a very sad day for the Sharp family and the city of Creston as a whole,” Ver Meer said. “We’ll work through this together.”

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Novedades Quintana Roo, a news outlet in Cancun, reported that employees had entered the Sharps' room after noticing an odor.

The Sharps' stay at the hotel was scheduled between March 14 to March 21, according to the news outlet.

An advisory on the State Department's website last updated this month advises caution for Americans traveling to Mexico.

Timeline

MARCH 14: The Sharp family of Creston leaves the United States for Tulum, Mexico, for a vacation, according to relatives. Amy Sharp tells relatives they made it safely.

MARCH 17: Amy Sharp's Twitter account retweets an update about a college softball game, the last indication of the family's activity visible publicly on the internet. Both parents limited which of their Facebook posts were visible to the public; relatives did not say Friday when the most recent posts were published.

MARCH 21: The Sharps were scheduled to leave Cancun, Mexico, on an afternoon flight to St. Louis.

MARCH 22: The Southwestern Community College men's basketball team plays in the National Junior College Athletic Association Division II tournament in Danville, Illinois. The Sharps were expected to be in attendance; relatives are concerned when they are not present. The family eventually decides to contact law enforcement.