A Billerica man previously convicted on child rape charges pleaded guilty Monday to an additional count of possession of child pornography after his 2022 arrest. Eric Robert Johnson, 50, of Floyd Street in Billerica gave a guilty plea to U.S. District Court Judge Denise J. Casper. Johnson had been arrested and criminally charged with possession of child pornography in February, 2022, and he was subsequently indicted that March by a federal grand jury. He is now scheduled for sentencing on May 2.