A former Calgary police constable has pleaded guilty to accessing more than 4,000 images of child pornography while he was employed by the service.

Thomas Buttle, 33, was arrested in March and charged with three child porn-related offences. On Tuesday, he pleaded guilty to one charge; the other two will be withdrawn at sentencing.

Buttle, who was a four-year member of CPS, appeared in court with his wife.

At the time of his arrest, CPS said Buttle had been placed on administrative leave pending the outcome of his trial. CBC News requested an update on his status with the service and was told on Tuesday that he had resigned several months earlier.

Defence lawyer Alain Hepner and prosecutor Jenny Rees told provincial court Judge Frank Maloney a sentencing hearing would take place in May after a psychiatric risk assessment is completed.

Buttle is facing a minimum of six months in jail.

According to an agreed statement of facts, the investigation began in January after Tumblr reported to the U.S. National Center for Missing and Exploited Children that seven images of child pornography had been uploaded by a user in southern Alberta.

The information was forwarded to local ICE investigators, who then tracked the IP address to Buttle.

A search warrant was executed and several electronic devices were seized from Buttle's home, where he was taken into custody.

Investigators found child pornography on four electronic devices. In total, officers found more than 4,000 child pornography images, all of which had been deleted.

The illegal images were found on two cellphones, a computer tower and a laptop.

"The accused admits that he intentionally accessed the child pornography found on the four devices," reads the agreed statement of facts.

Buttle remains on bail until he is sentenced.