The odor “lit up the whole street,” she said.

The smell grew stronger closer to Mr. Williams’s apartment, on the first floor of a light-blue, three-family house. Ms. Douglas said the odor coming out of Mr. Williams’s home was hard to ignore, even when she closed her windows to hinder it.

“That smell there. It was real ripe,” Ms. Douglas said. “The minute you opened that door, it was there.”

Mr. Williams’s upstairs neighbor, Hakeema Christopher, said she had caught a whiff of the odor as early as July. When she complained about the stench, she said, Mr. Williams responded by giving her cleaning supplies and a sponge.

The Newark police began investigating Mr. Williams for sexual abuse after receiving a call from the 13-year-old boy’s father, a police official said on Monday. The abuse began last year, prosecutors said, and involved multiple encounters over several months.

Officers at the apartment on Monday were shocked by the gruesome discovery of the remains, the official said, and dogs were called in to sniff out other remains. In addition to a plastic bin with the mummified remains, the police also found a spine with an intact rib cage and a bag of bones, all of which were believed to belong to the same corpse.

Officials were not sure to whom the remains belonged or from where they came. The regional medical examiner’s office was investigating them, hoping to determine more information about their origin, said Katherine Carter, a spokeswoman for the Essex County prosecutor’s office.

The remains were not believed to be directly linked to the sexual abuse, officials said. Mr. Williams told detectives that he purchased them and used them for religious rituals, the police official said. In addition to the human remains, officers found an altar “to an unknown deity” in Mr. Williams’s bedroom.