Could my 18 year old Marine nephew go to prison?

Source: My Nephew ( A Proud Marine...Somewhat ) He states in Boot camp ( 5 months ago ) they all said "Kill Iraqi People" Or Kill Arabs" and they got a pat on the back. Now, this Marine By the name of Pennington that "Yell" Came back to haunt him...got 8 years in prison. Read On...During Pennington's plea-agreement for 8 years and sentencing hearing, prosecutors played video footage that showed him making statements about wanting to "kill Iraqis". ( This came back to hang him ) In addition, a co-defendant testified that Pennington mocked Awad's bullet-riddled brain and played with the man's hand as he put the corpse into a body bag. So, Could my Nephew go to prison if he fights in Iraq and kills the so called enemy that war supporters say is protecting the USA freedom.