CHICAGO — Haunted by the 2005 slaying of an Indiana schoolgirl, whose decapitated and dismembered body was found by boaters in a river near Chicago, federal and local officials appealed for the public’s help Wednesday in solving the crime.

At a news conference at FBI headquarters in Chicago, authorities declined to disclose whether new leads or suspects have emerged, saying only that there’s hope, with the passing of time, someone might now be willing to come forward with vital clues.

Investigators believe 13-year-old Alexandra Anaya knew her killer, the head of the FBI’s Chicago office told reporters, describing the girl’s killing as “one of the most heinous murders we have seen involving a child.”

Michael Anderson added about the killer: “Unfortunately, that person is still out there.”

Anaya’s torso was found wrapped in chains in the Little Calumet River on Aug. 16, 2005, three days after she was last seen alive leaving her Hammond, Indiana, home early in the morning. DNA testing confirmed the torso was Anaya’s.

A reporter asked one of the original Hammond police investigators at the same news conference if the case continues to haunt him. “Yes, it does,” said Ronald Johnson, who retired a year after the killing. “Many sleepless nights.”

A photograph of Anaya smiling on a staircase, a book at her side, sat on an easel a few feet away as Johnson spoke.

Family, friends and potential witnesses are being re-interviewed, and some physical evidence will be retested in hopes that advancements in forensics science can reveal something new that points to the killer, FBI officials told reporters.

Changing relationships over the 11 years may also make some witnesses previously reluctant to talk more willing to tell what they know, said the current lead investigator for the FBI, Courtney Corbett.

“Sometimes time works in the favor of an ongoing investigation,” she said.

Next to the picture of Anaya was a photograph of a gold chain with a crucifix that investigators said the girl was thought to be wearing the day she went missing.

A reporter asked Corbett if the killer, whoever it is, might be holding on to it or something else that belonged to Anaya.

“They very well could be,” she said.

A suburban Chicago man had been accused of molesting Anaya, according to court documents filed later in 2005. The man had lived with the girl’s mother, Sandra Anaya, but the couple broke up in the spring of 2005 after the girl accused the man of molesting her since age 7, court documents from that time say.

The man has never been identified as a suspect in the girl’s death. He was charged later in 2005 with interstate domestic violence against Sandra Anaya. A federal jury in Indiana, however, found him not guilty on all counts in a 2006 trial.

Asked about the man at Wednesday’s news conference and whether he might now be a suspect in the killing, officials declined any comment.