WESTMINSTER, Colo. - The weeklong search for a 10-year-old Colorado girl became a murder investigation after authorities identified a body found in a suburban Denver park as that of fifth-grader Jessica Ridgeway. "Our focus has changed from the search for Jessica to a mission of justice for Jessica," Westminster Police Chief Lee Birk said Friday. Anxious parents kept close watch over their children. Fueling the frustration: The FBI again urged residents to report any suspicious activity by people they know. "We want you to look for changes of habits, patterns, peculiar absences of those around you and report it to law enforcement," said Jim Yacone, FBI special agent in charge in Denver. The U.S. Marshals Service, immigration officials and state Department of Corrections were reviewing registered sex offenders in the area, Yacone said without elaborating. Investigators have received more than 1,500 tips from the public. Authorities also have searched more than 500 homes and more than 1,000 vehicles but still need the public's help, Yacone said. Jessica was last seen beginning a short walk from her home to Witt Elementary School on the morning of Oct. 5. She never arrived. A search by hundreds of law officers did not start until hours later because Jessica's mother works nights and slept through a call from school officials saying Jessica wasn't there. Jessica's backpack was found on a sidewalk in Superior on Oct. 7, some 6 miles northwest of her Westminster home. On Wednesday, authorities discovered a body in Arvada, about 7 miles west of her home, in a park in Arvada. They announced the body was Jessica's on Friday. Over the week, police said Jessica had been abducted. They don't suspect her parents, Sarah Ridgeway of Westminster, and Jeremiah Bryant of Missouri. Signs of the tragedy are everywhere in Jessica's neighborhood of modest, two-story homes with single-car garages. Officers have searched homes and yards and guarded crosswalks. They've photographed cars entering the neighborhood. Law-enforcement leaders said they would not disclose more information, saying it would jeopardize the investigation. The FBI said they have not ruled out that the search for the suspect could be national. People kind of don't know what to expect because we don't know where this guy is or who he is or what he's capable of doing. That's the most horrible thing," said Suzette Morgan, a mother of two boys ages 13 and 8. Lisa Kempton's three boys attend Jessica's school. "I just make sure that if they go out that they stick together," Kempton said. I'm trying not to live in fear, because ultimately that's when the crazies win. Mary Sherman, who has a 16-year-old son and two daughters ages 13 and 11, said she and her neighbors are ensuring that children are monitored by trusted adults as they walk to school or the bus stop. "We still have a fabulous community," Sherman said. We'll move on.