"That individual is under arrest and in custody," he said.
Haarup, 19, and Key, 22, were reported missing Friday from after Haarup's fiancé, Matt Meyers, came home to find his 6- and 18-month old daughters alone and in the same crib. Relatives of the women said there was blood on the couch in the Edgerton residence, located about 35 miles north of Kansas City.
"The truck was gone, the girls were gone and Matt has some personal guns that had been missing as well. That is all he had to tell me, and I knew something was wrong at that point," the mother of the missing women, Taresa Haarup, told KCTV.
The Platte County Sheriff's Department said Sunday that authorities were speaking with a person of interest in the case and have executed two search warrants.
The missing truck was found parked on a gravel road Saturday, prompting authorities to search the surrounding fields. Although there were no signs of foul play, the truck was towed to the Kansas City crime laboratory to check for evidence.
The sisters' father, Paul Haarup, begged for his daughters' safe return during a candlelight vigil Saturday night that drew a crowd of about 70 people.
"Whoever has them, give them a phone, have them call us, put an end to this," Haarup told KSHB.
Family members fear the sisters were abducted. They said Key, the mother of a 4-year-old girl, had been running with a bad crowd and sought her sister's help turning her life around.
"That's why she came to Britny and Matt's house; to get help, to get out of that lifestyle. She was very serious about getting help," Cassandra Meyers, sister-in-law of Matt Meyers, told KSHB.
Haarup's fiancé said his daughters need their mother back home.
"Your babies love you and they miss you," he told The Kansas City Star.