Police said Monday they will return to the neighborhood where a 6-year-old Tucson girl was reported missing a month ago in hopes of speaking with residents who may not have been interviewed when the area was originally canvassed.

Tucson Police Lt. Fabian Pacheco told reporters at an afternoon press conference that officers investigating the disappearance of Isabel Celis also plan to re-interview all of the Level 2 and Level 3 sex offenders nearby whose crimes targeted children under 10 years old. They have spoken to more than 540 registered sex offenders since Isabel was reported missing on April 21.

Pacheco said police will distribute a new flyer that asks several questions of people living or working in the general vicinity of the Celis home:

•     Did they see anything unusual before or since Isabel’s disappearance?
•     Were there delivery people or solicitors in the area during that time?
•     Has there been construction in the area?
•     Were there any yard sales, parties or other large gatherings before the incident?
•     Did they notice any unusual vehicles in the area prior to the disappearance?
•     Do they or their neighbors have surveillance camera at their homes?

Isabel’s parents, Sergio and Becky Celis, told police that she vanished from her bedroom in the middle of the night after they put her to sleep on April 20. In his 911 call, Sergio Celis said he went to wake her around 8:00 a.m. on April 21, but she was gone and her window was open with the screen lying in the backyard.

According to Pacheco, police are still considering the possibility that Isabel was abducted by a stranger, but they have not ruled out anyone, including family members, as suspects. He said the Celis family has been cooperating with the investigation so far and he hopes they will continue to do so.

Pacheco also announced that Monday’s press briefing was the last regularly scheduled update on the case police will be holding.

At a vigil over the weekend, Becky Celis spoke out in defense of Sergio, who has not been charged or named as a suspect in the case. He recently reached a voluntary agreement with Child Protective Services to stay away from their other two children. Authorities have not commented on what led to that decision.

“He’s a great husband, a great father to the boys and to Isabel,” Becky Celis told KGUN. “At the end of the day when Isabel comes home, everybody’s questions will be answered.”

For the latest news on the case, watch Nancy Grace Tuesday at 8 p.m. and 10 p.m. ET on HLN, or go to www.HLNtv.com