CAMDEN, N.J. -- A New Jersey teenager has admitted plotting to kill Pope Francis when he visited Philadelphia in 2015.

Seventeen-year-old Santos Colon Jr. pleaded guilty as an adult to attempting to provide material support to terrorists. The Lindenwold resident faces up to 15 years in prison.

Federal prosecutors say Colon admitted plotting the assassination during a nearly two-month period in the weeks leading up to the pope's visit. The plot involved using a sniper to shoot the pope during a Mass and setting off explosive devices nearby.

Colon engaged someone he thought would be the sniper but was an undercover FBI employee. Prosecutors say Colon engaged in target reconnaissance with an FBI confidential source and instructed the source to buy materials to make explosive devices.

Prosecutors haven't identified a motive.

Sentencing hasn't been scheduled.