Police served a fresh arrest warrant Monday on a 41-year-old man for allegedly throwing a 9-year-old boy to his death from the top floor of a condominium complex in Tama Ward, Kawasaki.
Kenji Imai has already been indicted for attempting to kill a 68-year-old female custodian in the same building.
He had reportedly told police that he wanted to kill himself and had thought about killing a child.
"I visited the condominium eight days prior to murdering the boy to prepare to kill someone," Imai was quoted by police officials as saying. "When I went back to the 15th floor, Yamakawa was there, so I killed him."
However, it is not clear why he killed the boy, and police said they suspect Imai's suicidal desire may have somehow turned into a lust to kill indiscriminately.
Police believe Imai threw Yuki Yamakawa, a third-grader at a local elementary school who lived on the 14th floor of the building, from the 15th-floor walkway on March 20.