The schizophrenic Brooklyn man charged with killing his 4-year-old brother by dropping him off a seven-story building told cops he selected the sibling because he was the “lightest” family member, according to newly unsealed court documents.

“I thought that God would make the world a better place,” Shawn Smith, 20, explained when asked why he killed sibling Shimron at their family’s Midwood apartment building last month.

Smith said he chose the tot because “he was the lightest, and he was in the easiest position.”

There were three other kids in the apartment, including a 5-year-old.

Smith was arraigned Thursday on charges of first-degree murder. Attorney Jonathan Strauss pleaded “not guilty” on his behalf.