The motive for killing the Texas boy found lying dead on a Dallas street on Saturday remained unknown even after the suspect for the heinous crime was already placed under the custody of authorities. 

Authorities identified the 4-year-old boy as Cash Gernon, who was discovered by a passerby taking an early morning walk.

Since the beginning of the investigation, authorities already suspected a murder case due to the multiple stab wounds the Texas boy had sustained. Cash Gernon was pronounced dead on the scene by police.

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Suspect Arrested For Death of 4-Year-Old Texas Boy

Dallas Police Department identified the suspect as 18-year-old Darriynn Brown. People reported that the teenager was arrested by the authorities on Sunday and was charged with kidnapping and burglary. 

Dallas investigators were also anticipating additional charges to be filed against Darriynn Brown.

"Even us as police officers, we are shocked," said police executive assistant chief Albert Martinez, who also expressed anger about the toddler's death at the hands of the suspect.

New York Daily News reported that surveillance footage inside a Dallas home revealed that Darriynn Brown picked up Gernon from his bed on Saturday morning and then carried the Texas boy away from the residence. 

Cited an arrest affidavit, People reported that the teenager took Cash Gernon away from the residence while the Texas boy was sleeping. 

About two hours later, Gernon was found dead on the street, just blocks from his home. Brown was caught in the video surveillance cameras inside the home that filmed the kidnapping.

The Dallas Police Department disclosed that Gernon and his twin brother live in the home of their biological father's girlfriend, Monica Sherrod.

"I'm confused," said Sherrod's son, Kamron Mori, 18. "Who does this to a 4-year-old kid?"

What is the Relationship Between Darriynn Brown and Kamron Mori?

It is still unclear what is the motive of Brown to the Texas boy that he allegedly kidnapped. However, reports revealed that Mori and Brown went to Duncanville Junior High and High School together, and they had once been friends.

"Friends are nothing," Mori told Dallas News. "Evil. No reason. Literally, no reason," he said about the killing of Gernon connected to his schoolmate.

Reports revealed that Gernon and his twin brother are staying with Sherrod because their biological father was missing since March, and she could not track him down. 

On Monday, officers revealed that Melinda Seagroves, the biological mother of the Texas boy and his twin brother, was trying to locate her children and the father, who took the toddlers earlier this year. The Texas boy's twin brother has since been reunited with Seagroves.

Although the motive for killing the Texas boy is still unknown, Brown is held in Dallas County jail on a $750,000 bond. The suspect has yet to enter a plea.

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WATCH: Cops: 18-year-old Took Dallas 4-Year-Old From His Bed Hours Before His Death - From FOX 4 Dallas-Fort Worth