Timeline: Man indicted in the killing of 2 Tucson girls

In 2012, 6-year-old Isabel Celis went missing from her midtown home. The incident happened at night as the family slept. No one heard any sounds.

Isabel's father, Sergio, reported Isabel missing the following morning on April 21, 2012, after searching for her with her two older brothers.

They found her bedroom window open.

Her disappearance shook the city of Tucson, as the community united to help find her. Tucson police received thousands of tips throughout their investigation.

In June of 2014, 13-year-old Maribel Gonzalez told her family she was going to visit a friend. 

When Maribel didn't come home the following morning, her mother called the friend who told her that Maribel never arrived. 

Maribel was reported missing and was initially treated as a runaway, Arizona Daily Star archives show.

Maribel's home was said to be minutes away from Isabel's. 

Just a few days later, Maribel's body was found in a desert area northwest of Tucson, near North Trico and West Avra Valley roads.

There were no suspects at the time. 

Years after Isabel went missing, her remains were found northwest of Tucson — in roughly the same area as Maribel's body.

Police Chief Chris Magnus informed the public of their discovery on March 31, 2017, though the remains were found earlier in the month. 

Officials remained tight-lipped about the case and would not discuss how investigators were led to Isabel's remains.

On Sept. 14, 2018, 36-year-old Christopher Matthew Clements was indicted. He is accused of killing both Isabel and Maribel. 

Authorities announced the indictment the following day, Sept. 15. They revealed that in 2017, FBI agents received a tip about a man who might know more information about Isabel's disappearance.

Clements, a convicted sex offender, was the man. 

After speaking with Clements, investigators were able to find Isabel's remains.

Clements is facing 22 charges that include two counts of first-degree murder, two counts of kidnapping of a minor under age 15, burglary, and 14 counts of sexual exploitation of a minor, which is said to be related to child pornography. 

He is currently being held in the Maricopa County jail on unrelated charges.

Records show that Clements has a long criminal history and that he was out of jail on bail when Maribel was killed.

On Sept. 21, 2018, the Star obtained new court documents showing that Clements led investigators to Isabel's remains after asking for unrelated burglary charges to be dropped.

He also asked that his impounded car be released. Investigators agreed to his terms. 

The same court documents show that DNA taken from Maribel's body was linked to Clements. 

They also say that investigators found a letter from Clements that implied there were four bodies left in the desert area.

Investigators also found schoolwork and a child's purple sweater in the home of Clements' girlfriend. Sexually explicit photos of children were found on a computer, in addition to internet searches such as "child killer found not guilty" and "body found in desert."

Clements pleaded not guilty in a court appearance at Pima County Superior Court on Sept. 24, 2018.

Families of Isabel and Maribel were in the courtroom for the video arraignment. 

Clements appeared to have a black eye. The week prior, officials confirmed that he had gotten into a fight with two other inmates at the Maricopa County jail.