While in high school, he played football and was part of the police explorer program, said another neighbor, City Councilman Gerard Goedhart.
He went to college at Southern Utah University, where he was a running back on the school's football team and graduated with a degree in political science in 2001, Southern Utah athletic department spokesman Neil Gardner said.
"Chris Dorner is the last person I would ever think would do such," Gardner said Thursday. "He was a great kid."
College classmate James Usera said Dorner called him "out of the blue" four years ago, after not having spoken for several years after graduation. He complained about problems with the LAPD during the call, but Usera didn't recall the details.
"He did seem to be bothered by it or upset by it a bit, but certainly nothing that he said to me struck me as being a concern other than for concern for his employment," Usera told CNN.
He described Dorner as "a perfectly rational human being," "smart and insightful."
"Never anything that I experienced in a million years would lead me to conclude that this horrendous activity that he engaged in at this point was ever imminent or would ever be any type of concern," he added.
Dorner joined the Navy after college, receiving a commission as an ensign in July 2002. He trained in river-warfare units and and served a 2006-2007 stint in Iraq guarding oil platforms, according to Pentagon records. He held a commission as a lieutenant until February 1 and was rated as a rifle marksman and pistol expert, according to the records.
He enrolled in the LAPD Academy in February 2005 and spent four months on the streets as a trainee before being recalled to active duty for his stint in Iraq, police records state. In the end, the LAPD cost him not only his police job but his career in the Navy, he wrote.
"This is my last resort," he wrote. "The LAPD has suppressed the truth, and it has now led to deadly consequences."