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

Santa Clara County Sheriff’s Investigators have arrested a 21-year-old man in connection with the disappearance 15-year-old Sierra LaMar who disappeared on her way to a school bus stop.

Antolin Garcia-Torres / Santa Clara County Sheriff

Antolin Garcia-Torres, 21, has been booked into the Santa Clara County Jail on one count of murder and one count of kidnapping. At a press conference today, Sheriff Laurie Smith said that Garcia-Torres is responsible for the kidnapping and murder of Sierra “based on direct and circumstantial evidence including forensics analysis.” Police say that the discovery of Sierra’s cell phone, clothing, and personal belongings she wore on the day she disappeared contributed to their belief that Sierra was a victim of murder. Police also reveal they have physical evidence linking Sierra to the suspect’s vehicle. On May 8th, police announced they were searching for a Red Volkswagen Jetta connected to Sierra’s disappearance. Police say that Garcia-Torres is the owner of the Red Volkswagen Jetta that was seen near the area where Sierra was last seen during the time she went missing.

Sheriff Laurie Smith said that Sierra’s bag found near her home contained DNA belonging to Garcia-Torres. The DNA was then placed into the system and subsequently led police to the suspect. As a result, police put Garcia-Torres under 24-hour surveillance, and police hoped he would lead them to Sierra. Sheriff Laurie Smith said they believe “this was purely random…a stranger abduction of a young girl.”

According to police, forensic evidence has also linked the suspect to a separate assault in the Morgan Hill area from three years ago in March 2009.

Investigators say they have gained “some value” from their interviews with the suspect and hope that at some point he eventually tells them more. Right now police believe he is “the only person responsible for the kidnapping and murder of Sierra.” Sheriff Laurie Smith announced that they have not located any blood or a weapon. HLN reached out to Antolin Garcia-Torres’ attorney for a comment, but calls were not immediately returned.

At the end of the police press conference, Sierra’s mother made a plea to the suspect, begging him to “come forward and say where she is, and end this nightmare for us as a family.” Sierra’s mother said she’s not giving up hope because Sierra's body has still not been found.

Marc Klaas, whose 12-year-old daughter Polly was kidnapped and murdered, said his volunteers will continue to search until Sierra is found.

Sierra LaMar is a white female with an olive complexion. She is 5’2”, with a thin build and has long dark hair. If you have any information, please call the tipline at 408-808-4431 or email tips@sheriffsccgov.org. There is a $50,500 reward.

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

Police confirm they have discovered the body of a missing 19-year-old girl who investigators say disappeared after having a verbal argument with her boyfriend. HLN spoke with Euless Police Lt. Eric Starnes who said Valladares’ boyfriend is fully cooperating with the investigation and has not been named a suspect.

A man walking his dog discovered the missing teen’s decomposed body in a wooded area about 150 yards from the apartment complex where she was last seen alive, according to police.

“The body was decomposed, and we cannot tell if there was foul play or if the person died of natural causes,” according to police spokesman Lt. Eric Starnes.

The medical examiner’s office identified the body as Ashley Valladares through a fingerprint. No cause of death has been determined and police are not calling the death a homicide.

The night she went missing, Valladares had worked late at her job at a local KFC. When her shift ended at 11:15 p.m., Valladares went home to the apartment she shared with her boyfriend. Valladares’ boyfriend told police that he got upset with her and left their apartment around 11:30 p.m. because an unidentified man showed up asking for a haircut. Valladares reportedly chased her boyfriend out of the apartment and begged him not to leave. Her boyfriend told police he returned home around 2:00 a.m. but she was gone.

Valladares’ father reported her missing after her boyfriend told him that she never came home, according to police.

Anyone with information is urged to contact the Euless Police Department at 817-685-1556.

COTTONWOOD, CA – The body of Karen Duenas, a mother of five and college instructor, was discovered by her husband in the bedroom of their upscale home. Police say she was stabbed to death multiple times.

Karen Duenas’ husband, Mark Duenas, called 911 in the early morning hours of May 5th to report he found his wife with a large gash in her chest. Mark Duenas told the 911 dispatcher that there was “blood everywhere.” The murdered mother of five was pronounced dead at the scene. Her husband told police he didn’t know what happened to her.

Police will not reveal what type of murder weapon was used in the horrific stabbing death or if there was any sign of forced entry. Neighbors reportedly say they didn’t see anything suspicious in the area around the time of the murder.

Karen’s grieving family, friends and students honored her at a memorial at Shasta College on May 11th. Karen’s brother told mourners that her husband couldn’t attend.

Extensive searches have been conducted in the area for additional evidence. Divers searched an irrigation canal just three blocks from the home. Police were seen removing brush behind the family home, but reportedly didn’t find any additional clues.

HLN reached out to Mark Duenas, but he declined to comment. Police say he is not a suspect in his wife’s murder.

Karen Duenas leaves behind five sons and five grandsons. She was an instructor in the agriculture, industry and technology division at Shasta College. She has just finished her first year of nursing school.

In a statement released by Shasta College, faculty said Karen Duenas was an “amazing instructor and beautiful human being” who was “loved by everyone.”

Anyone with information regarding the murder of Karen Duenas is encouraged to contact the Shasta County Sheriff’s Office at 530-245-6157. There is a $10,000 reward.

For more on the case, watch Nancy Grace Friday at 8 pm and 10 pm ET on HLN, and for all the latest news, go to www.HLNtv.com.