( CNN ) -- A friend said Monday that `` something happened '' to the man police accused of killing four homeless people in California , after he came back from serving in the U.S. military in Iraq . `` He was a little bit more serious , it seemed like there was something on his mind , '' Brian , who lived a few doors down from Itzcoatl Ocampo and asked to be identified only by his first name , told CNN . `` He seemed really depressed and down , and things in his life were n't looking that well . '' The 23-year-old Ocampo was arrested Friday night after he allegedly stabbed a transient to death in Orange County , Anaheim Police Sgt . Bob Dunn said Sunday . The suspect has not been arraigned in relation to that or the three other killings , and police have not detailed evidence behind their accusation . His father , Refugio Ocampo , who lost his home in 2008 and now lives in the cab of a semi-trailer parked in Fullerton , California , said it was hard to believe his son could be involved in the killings . `` I saw him so many times giving the last money he had in his pocket ... to the homeless , to the people that ( are ) asking for some help . ... My son 's always been a role model , '' Ocampo said in a video interview posted on the Orange County Register 's website . Ocampo , 50 , told the Register that his son , worried about his father 's safety , had recently pointed out an FBI warning about homeless men being killed in the area . Refugio Ocampo said his son was a Marine in Iraq , and returned a changed man . He started talking about things that `` did n't make any sense , '' like the end of the world . U.S. military officials did n't immediately respond Monday to CNN requests for information about Itzcoatl Ocampo 's military service . `` They killed the person he was , '' he told the Orange County Register . `` And that 's the only possibility I can think of that he would do something like that . '' Brian , the neighbor , described Itzcoatl Ocampo as a `` fun , ... ordinary kid '' when they grew up together in southern California , adding `` he was really looking forward to the service '' after graduating from high school . `` When you were around him , you had fun , '' the suspect 's high school classmate said . But like Ocampo 's father , Brian said he noticed some recent changes in the young man , including when the two met up a few times last summer . `` I knew he wanted to see ( combat ) action , and I knew he enjoyed it , '' said Brian , noting he 'd lent his friend a self-help book . `` Then something happened , and I just do n't know what . '' Brian added that he had a hard time reckoning that his friend possibly could be responsible for the killings . `` I would never have guessed this , '' he said . Ocampo , 50 , told the Register that his son , worried about his father 's safety , had recently pointed out an FBI warning about homeless men being killed in the area . Refugio Ocampo said his son was a Marine in Iraq , and returned a changed man . He started talking about things that `` did n't make any sense , '' like the end of the world . U.S. military officials did n't immediately respond Monday to CNN requests for information about Itzcoatl Ocampo 's military service . `` They killed the person he was , '' he told the Orange County Register . `` And that 's the only possibility I can think of that he would do something like that . '' Brian , the neighbor , described Itzcoatl Ocampo as a `` fun , ... ordinary kid '' when they grew up together in southern California , adding `` he was really looking forward to the service '' after graduating from high school . `` When you were around him , you had fun , '' the suspect 's high school classmate said . But like Ocampo 's father , Brian said he noticed some recent changes in the young man , including when the two met up a few times last summer . `` I knew he wanted to see ( combat ) action , and I knew he enjoyed it , '' said Brian , noting he 'd lent his friend a self-help book . `` Then something happened , and I just do n't know what . '' Brian added that he had a hard time reckoning that his friend possibly could be responsible for the killings . `` I would never have guessed this , '' he said . CNN 's Gabriel Falcon contributed to this report .
NEW : A friend says ` ` something happened '' to Itzcoatl , after a military tour . NEW : He says the once fun - loving man became preoccupied and ` ` depressed '' The suspect 's father read a paper that his son , himself , was homeless . The suspect is accused of killing two homeless men in Southern California .