Almost two years ago, Matthew Riskin Bean joined an online "mob" of anonymous individuals on the website 4chan.org in an effort to drive another adolescent to commit suicide.

Bean pleaded guilty in September to a single count of stalking after e-mailing a school the photos that a student had posted to the site of his erect penis.

Bean, 20, of Bergenfield, N.J., claimed in the e-mail that he was the "concerned mother" of another boy at the school and that "this sort of behavior [should not be] allowed to run rampant," court papers said.

That was the extent of Bean's involvement in what Assistant U.S. Attorney Michael Levy called a case of "cyberstalking or bullying."

U.S. District Judge Anita Brody said Tuesday that "it is important that people understand this is a crime" and sentenced Bean to 45 days in jail. He is to surrender to the Bureau of Prisons on March 4.

In 2003 or 2004, a now-18-year-old college student from the Philadelphia region, identified in court papers only as "Person No. 1," spent time in an online chat room and uploaded the graphic photos to trade with others.

When Bean came upon comments about the photos on 4chan - a so-called imageboard site notorious for its lack of rules and adult supervision - he sent an e-mail with the images of Person No. 1 to the boy's school.

[][]Court papers said Bean told FBI agents during an interview in his home on Sept. 24, 2009, that he had participated in an online discussion regarding the boy, in which he and others attempted to identify him. Other participants - though not Bean himself - expressed the hope that if the pictures got to the boy's school, he would commit suicide.

Before sentencing, Bean was remorseful and said the pain he has suffered was "nothing compared to the pain I caused [Person No. 1]."

Levy said a brief sentence of incarceration was necessary to deter others from similar conduct.

Defense attorney Donald Goldberg argued that Bean's arrest was a "significant wake-up call" and incarceration would stymie Bean's ongoing rehabilitation.

"Give us a chance to save this shy, very vulnerable young man, who is sweet beyond belief," Goldberg pleaded.

The defense attorney argued in court papers that putting Bean in the slammer - even for a brief period of time - could potentially subject him to sexual assault.

Bean is 5-foot-4 and weighs 110 pounds, Goldberg said. Brody said she thought he was 12 or 13 when she first saw him.