WASHINGTON — The former federal police officer who caused an explosion at a Gaithersburg, Maryland, science lab while cooking meth pleaded guilty in U.S. District Court in Greenbelt Friday.

Christopher Bartley, 41, will be sentenced Nov. 19 under a plea deal in which he could get 20 years.

Bartley claims he was not making meth for personal use. He says it was part of an unauthorized training experiment.

The explosion happened July 18 on the campus of the National Institute of Standards and Technology. Bartley was a lieutenant and supervisor with the institute’s police force; he resigned the day after the explosion.