Updated at 4:30 p.m. Thursday: Revised to include additional arrests.

Dallas police have arrested 12 men in two weeks as part of an extensive investigation into child pornography traded online.

The arrests are part of a larger crimes-against-children investigation in which local and federal authorities arrested 28 people, 20 of them accused of possessing pornographic images of children.

Police said six were arrested on child trafficking charges, one was arrested on an online solicitation of a minor charge and another was arrested on a charge of sexual performance of a child.

Police say they also rescued one victim in the operation but did not release details.

Arrest records show 12 Dallas men have been accused of having or sharing child pornography since Aug. 28. Details weren't available on each case.

The Dallas police investigative unit works with the North Texas Crimes Against Children Task Force, which receives $60 million in federal funding a year. The task force is authorized under the Protect Our Children Act.

The Dallas Police Department recently launched in-house forensic testing to help detectives track down who places online ads selling children for sex or posts sexual images of children online.

From top left: Alexander Valdez, 23; Anthony Estes, 44; Chester Miller, 64; Daniel Garner, 33; John Galanopoulos, 33; Juan Galviz, 20; Leonardo Velazquezmarin, 21; Miguel Calixto, 19; Misael Lopez, 36; Paul Coleman, 36; Ronald Castillo, 24; and Steven Nagle-Perkins, 62. (Dallas County jail )

Those recently arrested on felony child pornography possession range in age from 19 to 64.

One man, 36-year-old Misael Lopez, pleaded guilty in June to four counts of possession of child pornography. He was given 10 years' probation. He faces three new counts of possession.

Arrest warrants for the men reveal graphic details of the types of images and videos they had saved on laptops, hard drives and in online accounts.

Steven Nagle-Perkins, 62, Anthony Estes, 44, and Daniel Garner, 33, were arrested this month on felony possession of child pornography charges. Miguel Calixto, 19, was arrested Aug. 28.

Police found multiple images on the computers connected to their Dallas homes, according to arrest records.

The men's cases are not connected.

Detectives from the Dallas Police Department's internet crimes-against-children unit searched the homes after receiving tips that pornographic images of children were shared or saved on the men's computers.

Police found a computer in Nagle-Perkins' home that contained several images of boys and girls between the ages of 8 and 12 in sexually explicit poses. The man's wife told police Nagle-Perkins is the only person to use the computer that had the images, an arrest warrant affidavit says.

His wife also told police that she would be shocked to learn her husband was looking at images of toddlers but said she "would not be shocked to learn that her husband was viewing 13-year-old children," the warrant says.

Nagle-Perkins told police that he chatted online under the username "dallasnastyman000," the warrant says.

In Estes' Dallas home, police found a briefcase in the master bedroom closet that contained an external hard drive. The hard drive had several images of adults raping children, according to an arrest warrant affidavit.

Police also took a laptop from the home. Investigators estimated the laptop and external hard drive contained thousands of pornographic images of children and child erotica, the warrant says.

The sexual images were of children ranging from 2 to 12, the warrant shows.

Garner was arrested after police received a tip that someone had uploaded a photo of a toddler being raped onto an online chatroom, according to his arrest warrant affidavit. Investigators traced the image to an internet account he used.

Police found a laptop in Calixto's Dallas home that had three pornographic videos of children. Two of the videos showed girls under 12 being raped by adult men. Another video showed two young girls forced to perform sexual acts on each other.

Garner was booked into the Dallas County Jail on Friday and was released Sunday.

Nagle-Perkins remains in the Dallas County jail in lieu of $300,000 bail. Jail records show a second case will be filed against him.

Estes remains in the Dallas County jail in lieu of $150,000 bail.