(CNN) -- A South Florida teenager accused of killing and mutilating 19 cats excitedly described to police how he dissected cats in class, and where to find cats for experimentation, according to police.

Tyler Weinman laughed when police told him they had information he was the cat killer, an arrest document said.

When Miami-Dade police told Tyler Hayes Weinman someone was killing cats in the neighborhood, the 18-year-old reacted by laughing, according to a newly released arrest affidavit made public Monday.

Most of the cats were found in their owners' yards. "One appeared to be posed with a slit down the middle of its stomach," the affidavit states.

On Monday, Weinman pleaded not guilty to more than 40 criminal counts, including multiple charges of felony animal cruelty and burglary. He is out of jail on $249,500 bond and under house arrest wearing an electronic monitor, but is being held for 48 hours for a psychiatric evaluation.

The teen's attorney David Macey said there was a "lynch mob" after his innocent client and accused Judge Mindy Glazer of "prejudging" Weinman.

"He did not kill the cats," Macey told reporters outside the courtroom. "The individual who committed this crime is still running around out there."

The arrest affidavit, which a judge gave prosecutors until Monday to make public, reads like a grisly horror movie and indicates Weinman was knowledgeable of and fascinated with dissection of cats.

During questioning, according to the affidavit, a detective told the teenager that police were informed he was involved in the cat slayings. Weinman replied he heard about the cats and that he told his mother. He told police that a school he had been expelled from was the only school in Miami-Dade that taught how to dissect using cats, according to the affidavit.

The teenager went on to offer several other bizarre and unsubstantiated trivia, including saying that Mexico is the only source for cats used for dissection and describing their size.

Weinman "became excited and animated" as he told the detective about cat dissection research he had discovered on the Internet, the affidavit states.

"Weinman was asked to expound on what he meant and he repeated, with noted excitement, 'It just makes a certain sound, a tearing sound," says the affidavit.

The detective asked Weinman what tools might be used to commit animal cruelty, and teenager replied, "I don't know, but I'm sure they are very well hidden."

How did he think the cats were being captured? The teen answered, "They have to be either tranquilized or poisoned."

Weinman came to the attention of authorities in late April, the affidavit states, as cats began to go missing in a suburban Dade County neighborhood called Whispering Pines just outside Miami, Florida. Police had a few times seen Weinman walking and skateboarding in the middle of the night in the area, at least once wearing black clothing and carrying a dark backpack.

Detectives stopped the teenager and told him about the dead cats. Weinman responded by laughing, according to the arrest affidavit. He was not held at that time.

In May, the teenager was pulled over for a traffic violation and police found a "cutting instrument" on the ground beside his car. According to the affidavit, as an officer questioned the teen, he noticed what appeared to be a cat scratch on his arm.

"I got them from a stray cat that I feed at my mom's house," Weinman said.

The teen "was eager to show" the scratches and took off his shirt so that photographs could be taken, according to the questioning detective's account, which is detailed in the affidavit.

The teenager's divorced parents lived in separate neighborhoods, according to police. His mother resides in Cutler Bay. His father lives in Palmetto Bay, further north of Miami. According to the arrest affidavit, shortly after the teenager talked to police about dissecting cats, he went to live with his father who restricted his son's access to a car.

The killings shifted north as eight dead cats turned up in Palmetto Bay, police said.

At that point, police provided the teen's profile to the Miami-Dade Police Department's Psychological Services Section. Staff doctors met and discussed the case. They determined that the cat killer was likely male and suffered from some kind of conduct disorder.

If the killer was an adult, they concluded, that person would be classified as a sociopath.

In late May, police then got a court order to place a tracking device on the Honda Civic driven by Weinman. The affidavit states the car was tracked to the latest feline victim which had been skinned along the abdomen from the pelvic area to the hind legs. The pelt and genitalia were missing.

The cat killings became headline news across the country. Around that time, Weinman joined a Facebook page called "Catch-The-Cat-Killer."

The teenager is charged with 19 counts of felony animal cruelty, 19 counts of improperly disposing of an animal body and four counts of burglary. He's pleaded not guilty to all of the charges.

Kimberly Segal contributed to this report.

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