"We certainly would be interested in hearing from other people who may have concerns or whose children may have had interaction with this person," Laughlin said.
Authorities said investigators noticed similarities between the assault on the toddler and the attacks on the boy and his 12-year-old sister.
They put a rush on the DNA comparisons, which recently indicated that the attacks were carried out by the same person, Laughlin said.
On Aug. 13, Rivera allegedly was in the home of the toddler where the assault took place. Laughlin said relatives caring for the boy did not know about the assault until a day later, when he was seen by a doctor.
It was unclear why Rivera was in the house, but authorities said he knew the family.
Less than a month later, on Sept. 2, Dominick Andujar, 6, suffered a fatal neck wound that authorities said he received trying to protect his sister from Rivera in their Ware Street home. The girl was critically injured. Two other children in the house were not harmed.
Rivera was charged with murder, attempted murder, and sexual assault.
Rivera, who had been convicted of a drug charge stemming from 2006, had been required to submit a DNA sample for the national crime database.
Because there has been a backlog of cases, Rivera did not emerge as a suspect in the August case until after the two other children were attacked, authorities said.
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