A toddler’s decomposing foot was the first body part that appeared in the Garfield Park Lagoon. Soon, divers from the Chicago Police Department’s marine unit had retrieved the other foot, two arms and a head.

For the next 14 months, police investigated the gruesome murder of 2-year-old Kyrian Knox, sorting through witnesses and evidence until Monday, when they arrested Kamel Harris, 41, a man who was caring for Kyrian in September 2015 when the toddler was killed.

Police suspect Harris killed Kyrian because the lactose-intolerant toddler had drunk some milk and would not stop crying, according to the Chicago Tribune.

“It was pretty difficult to deal with,” Marine Unit Sgt. Angel Romero told the Tribune. “Probably one of the most difficult things I’ve dealt with in my 29 years on the job.”

Harris was charged with first-degree murder, concealment of a homicidal death and dismemberment of a human body. He is due to appear in Cook County bond court Wednesday.

“He kind of just snapped and couldn’t deal with it anymore,” Chicago Police Cmdr. Kevin Duffin said during a news conference.

In November 2015, shortly after Kyrian’s remains were discovered, police said they hit a wall in the investigation when a couple who was last seen with the toddler refused to cooperate, the Chicago Sun-Times reported. That month, DNA samples matched the body parts in the lagoon to Kyrian.

But near the end of the year, police made a breakthrough in the case when they obtained a search warrant for Harris’s vehicle, in which they found blood that tests would later link to Kyrian, according to the Tribune.

Lanisha Knox, Kyrian’s mother, left her toddler in Harris’s care after moving to Cedar Rapids, Iowa, with Harris’s daughter, a high school friend. Harris’s daughter also had a 2-year-old she left with her father; Duffin confirmed Tuesday the other child is safe.

Harris had denied that he ever brought Kyrian into his vehicle, telling the Rockford Register Star that someone he didn’t know picked up the toddler in late August.

Police have not determined the cause of Kyrian’s death, but they think he was killed in Rockford, where Harris lived with his girlfriend. According to the Register Star, Harris is charged in Cook County because the Chicago Police Department handled the investigation and found most of the evidence in Chicago.

Harris was in custody in Winnebago County on a separate charge when police arrested him Monday night, Duffin said.

Garfield Park is a few miles west of downtown Chicago. According to the Sun-Times, police suspect Harris made the drive from Rockford — about an hour and a half to two hours away — because he was familiar with the area.

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