Wichita ? Law enforcement officers in two states used high-tech tools to crack what they said they believe is the largest child porn case in Wichita history.

Steven Craig Perrine, 52, was charged this week with possession and distribution of child pornography after investigators said they searched his home and found more than 16,000 sexually explicit images involving children. Perrine was being held by federal authorities pending a detention hearing scheduled for Wednesday, and court records did not list any attorney as representing him.

Perrine already was serving probation after pleading guilty in 2003 to sexual exploitation of a child, admitting he had sexual images of a 7-year-old.

Authorities laid out their three-month investigation in an FBI affidavit filed in U.S. District Court in Wichita.

Authorities said the case began Sept. 9, when a Leetsdale, Pa., man visited an Internet chatroom and began talking to someone using the screen name “Stevedragonslayer.” The Pennsylvania man, who used the screen name “Dana-hotlips05,” said Stevedragonslayer asked if he wanted to see a “hot video,” FBI Special Agent Rebecca Martin wrote in an affidavit.

The video showed naked girls who looked younger than 10 walking around a bathroom, Martin wrote. Dana-hotlips05 called Leetsdale police and remained online “in hopes that an officer would arrive before the video ended,” Martin wrote.

Leetsdale officer Wayne Drish called officer Reginald Humbert, of the Pennsylvania State Police Computer Crimes Task Force, who works out of Moon, a township in neighboring Allegheny County 12 miles northwest of Pittsburgh.

“Police get a lot of calls from citizens,” Humbert said. “But I’d say calls of this kind are unusual.”

On Oct. 13, Humbert subpoenaed Yahoo Inc. for information on Stevedragonslayer. The company provided records six weeks later showing that screen name appearing 11 times. All the instances used the same Internet protocol address, registered to Cox Communications. By mid-December, Cox told police the account belonged to Perrine.

Detective Shawn Bostick, of the Wichita-Sedgwick County Exploited and Missing Child Unit, received Humbert’s findings and raided Perrine’s home on Dec. 22, seizing two computers.

FBI agent Martin wrote that a database maintained by the U.S. Department of Defense to help identify child pornography found that at least 406 files on Perrine’s computer matched images known to be real child porn – leading to Perrine’s arrest later that day.