The request by executive John D. Ryan in federal court in Wichita says he has no personal knowledge of the conduct at issue in the criminal case against Walter Ackerman, 56, of Lebanon, Kansas. Ackerman was indicted in November on charges of distribution and possession of child pornography.

U.S. District Judge Eric Melgren has scheduled a hearing for May 19-20 in Wichita to hear testimony on a defense motion to suppress as evidence the emails Ackerman allegedly sent containing child pornography. The defense argued that email provider AOL and the NCMEC were essentially acting as agents of law enforcement in violation of Fourth Amendment protections on illegal searches.

Prosecutors say AOL employs a process to systematically identify child pornography sent through its services. The company maintains a database of “hash values” — algorithms that act as digital thumbprints of electronic information — associated with child pornography. When it detects a file that matches a hash value in its database, the email is captured and sent to the National Center for Missing and Exploited Children. The agency then identifies the sender’s geographic location and notifies law enforcement.

The defense contends such a system used by AOL and some other email providers is akin to listening in on a telephone call, something that requires a wiretap warrant.

“Those ‘snooping’ eyes are not inherent in the process of creating and sending emails,” defense attorney John Henderson wrote in a court filing. “They are independently created to look at what Mr. Ackerman and others are sending in their emails over the internet. These mechanisms are independently created to look at the emails for a reason — to enforce the laws — law enforcement.”

Prosecutors countered that Ackerman did not have to use AOL and could have opted for another provider that does not scan message content. They noted that AOL is a private entity, citing a court ruling in a separate case finding the government exercises no control over AOL’s monitoring of its network, which is motivated by its own wholly private interests.

The government also argued that the NCMEC reviewed Ackerman’s email sent to its tip line to further its own ends as a charitable non-governmental organization aimed at protecting children. It says the NCMEC provides a conduit between Internet service providers and law enforcement.

Ryan, in asking that the defense subpoena issued to him to be tossed out, argued that a better witness would be John Shehan, the executive director of the NCMEC’s exploited children division and the person responsible for overseeing the cyber tip line. Prosecutors have already subpoenaed Shehan.