BANGOR, Maine — A Penobscot man who served 20 years in federal prison for bank robbery was sentenced Thursday in federal court to 7½ years in federal prison for possession of child pornography between July 2010 and July 2011.

Kevin Lee Ross, 52, was convicted of the charge in October after a jury trial, according to the U.S. attorney’s office.

Ross was released from federal prison June 24, 2004, after serving a 20-year sentence in federal prison for a 1983 bank robbery in Maine. Information about the bank robbery was not included in court documents and because the case is more than 30 years old, it is not available on the court’s electronic case filing system.

In addition to prison time, Ross was sentenced Thursday to five years of supervised release, according to information posted on the court’s electronic case filing system.

Investigators found 6,000 images and 300 videos on Ross’s computer of prepubescent children engaged in sex, including masochistic and sadomasochistic acts, Assistant Attorney General Andrew McCormack, who prosecuted the case, said in his sentencing memorandum.

Nearly 300 children were identified in the pictures and videos as victims of known sexual abuse, the federal prosecutor said. In all, Ross possessed images from 53 different known child pornography series.

The investigation into Ross began in July 2011 when a U.S. postal inspector monitoring a peer-to-peer file sharing network found files containing known child pornography being shared, according to court documents. The IP address was traced to the home Ross shared with his mother in Penobscot.

When officers arrived at the residence, they found a video of child pornography playing on one of Ross’ computers, the prosecution’s trial brief filed last year said.

Ross faced up to 10 years in federal prison and a fine of up to $250,000. McCormack recommend a 10-year sentence. Defense attorney Hunter Tzovarras recommended a sentence of between four years and three months and five years and three months.