Police investigating the disappearance of an Idaho boy missing for a week said Friday they are afraid the child may have been the victim of a tragedy.

Boise authorities told reporters that there are "suspicious circumstances" surrounding 8-year-old Robert Manwill's disappearance.

"Robert may be injured or be the victim of a tragic event," said Boise Police Chief Jim Kerns at a brief Friday press conference. "But he is still missing."

Earlier this week, news emerged that Robert's mother is on probation for fracturing the skull of the missing boy's infant half brother, who was removed from her custody by the state.

Robert was last seen near the Boise apartment of his mother, Melissa Scott Jenkins. Police detectives, FBI agents and more than 100 volunteers have searched extensively, but haven't found him.

Boise police have previously said there is no evidence of foul play in the disappearance of Robert, and that the family is cooperating fully.

The missing boy's father, Charles Manwill, has had custody of him since 2008. Jenkins has visitation rights, and the boy was visiting her the night he disappeared.

Court records show a history of family tragedies involving children.

Jenkins pleaded guilty in March to a misdemeanor charge of injury to a child following an October 2008 incident that fractured her infant son's skull, according to The Idaho Statesman.

Court records say Jenkins "did willfully inflict" the injury to her other son "by striking the child's head on a surface, causing a fracture to the child's skull," on Oct. 19, 2008. She was sentenced to 29 days of work release, fined $75.50 and put on probation for two years.

The child is the son of Jenkins' boyfriend, Daniel Edward Ehrlick, and was in the care of the state Department of Health and Welfare through at least February, according to court documents. The agency on Wednesday would not release his whereabouts, citing policy.

Jenkins has a third child, a 2 1/2-year-old daughter, fathered by a third man, who has custody of her. Jenkins has visitation rights. Ehrlick, who has been convicted of burglary, battery and possession of drug paraphernalia, is banned from being alone with the girl, but court documents don't say why.

In another case, Charles Manwill's wife, Silke Fatma Manwill, stabbed their 4-year-old son, Michael, in the chest in 1993, killing him. She was sentenced to federal prison after pleading guilty to voluntary manslaughter, and was released in 2002.

Meanwhile, Jenkins has declined to comment on her son Robert's disappearance.

"We are a joined family at this time in this crisis," said Trisha Burrill, Robert Manwill's aunt. "We are acting as one, with one goal in mind. To bring Robert back."

The Associated Press contributed to this report.