Walter Johnson, a former Wellesley High School girls cross country coach and assistant indoor/outdoor track coach, pleaded guilty in federal court on Monday, June 10, to a single count of possession of child pornography, according to a statement put out by Massachusetts U.S. Attorney Andrew Lelling’s office.

The next step is sentencing, scheduled for September 10, 2019. Johnson, 71, could get up to 20 years in a federal prison, a maximum fine of $250,000, and a minimum of up to a lifetime of supervised release, according to the statement.

In April 2017 after a track meet, the Wellesley Public School system issued an announcement by email that it had dismissed Johnson. At the time, the fact that Johnson wasn’t at the meet was unusual. The reason for his absence became clear when the school’s action was followed by a revelation by the U.S. Attorney’s Office that the then 69-year-old Framingham resident had been arrested and charged earlier that day with one count of distribution and one count of possession of child pornography. The arrest came after a months-long investigation.

Johnson’s arrest followed an investigation that started in January 2017 following information that child pornography was being traded on Craigslist. That investigation led to Johnson, and authorities said during a search of Johnson’s home, images and videos of child pornography were found on his computer and on a thumb drive hidden in his bedroom.

At the time of Johnson’s arrest, Superintendent David Lussier emphasized that all Wellesley High employees are fingerprinted and CORI checked before being hired. Johnson had no prior criminal record.

Following Johnson’s arrest, he was later indicted by a federal grand jury.

Johnson also was a special education teaching assistant at Wellesley Middle School from 2008 until 2015, and a former Harvard University track coach from the early 1980s until 2006.