(CNN) -- It's a common refrain heard from neighbors and friends after someone they know is accused in a mass shooting or other horrific crime: "He was such a nice guy! He was so quiet -- I can't believe he'd do something like this!"
Even serial rapist and killer Ted Bundy, who admitted to killing more than 36 women in the 1970s, was roundly described as charming.
And now accused cop killer Christopher Dorner seems to belong to the group of people who, if California authorities are correct, duped most everyone around them when it came to their sinister side.
"Chris was a guy who was approachable, had a great sense of humor, fun to be around, intelligent, good conversationalist, the kind of guy most people would want to hang out with and want to spend time with," said his friend and former Southern Utah University classmate James Usera.
"He was really, in my experience, a pretty terrific individual for whom I had a great deal of respect."
A former next-door neighbor also had a good impression of the accused killer, saying Dorner was "a nice, friendly guy, easy to approach."
Approachable, funny, terrific -- hardly the description you'd expect of a man who commanded a $1 million bounty after he promised a campaign of "asymmetric warfare" on the Los Angeles Police Department, his onetime employer.
Police say he followed through, killing four people, two of them police officers. He wounded four others. Authorities are now working to determine whether a body found in burned-out cabin near Angelus Oaks in Southern California belongs to the 33-year-old man who allegedly terrorized the force.
While Dorner gave off a certain impression to many, some who knew him best, like ex-girlfriend Ariana Williams, had seen another side of him.
Their relationship started when Dorner was a rookie cop in a tough, stress-filled beat, and ended with Williams posting a warning on a website for other women to avoid dating Dorner.
Williams was in shock at what unfolded this week, but was not completely surprised that Dorner was capable of acting out like that.
"When you see someone's behavior, and their manner of stress-induced behavior, coupled with how their personality already is, I think it makes it easier to understand why something like this could possibly happen," she told CNN Thursday.
He always kept weapons out in the open and nearby when he would visit her home, and lacked an even-keeled personality, Williams said.
She was not scared of Dorner, she said, but she had a persistent feeling that something wasn't right about him.
After their relationship ended, she felt compelled to go on the Internet and post a warning to other women who may date him in the future.
"Just in the general -- the fluctuation of his behavior, the swinging from the highs to the lows, the extreme nature of his personality," led her to say something, Williams said.
The killing rampage began February 3 after Dorner claimed he was railroaded out of the department after filing a brutality report against another officer. Dorner accused the LAPD of a longstanding culture of racism and misconduct that had worsened since the 1991 Rodney King beating.
In his purported manifesto, he levies several accusations against his former employer and, in one instance, demonstrates his willingness to exact violence on his co-workers.
After confronting an officer he claims used the n-word, Dorner claims to have grabbed the officer by the throat "and squeezed," but he writes that he regrets not doing more.
"What I should have done was put a Winchester Ranger SXT 9mm 147 grain bullet in his skull," the manifesto states.
There is not an abundance of personal detail in the manifesto, but he does allude to his background and beliefs.
He states he "never had the opportunity to have a family of my own" but doesn't elaborate, only issues a threat to the mothers, fathers, sisters, brothers and children of LAPD officers. He made good on that threat in at least one killing, that of a daughter of a retired officer, police say.
Dorner makes multiple references to his faith, or lack thereof. Again without elaborating, he states he is not a religious man and in a separate section of the manifesto mocks the Bible as "made of fiction and limited non-fiction."
"I'm not an aspiring rapper, I'm not a gang member, I'm not a dope dealer, I don't have multiple babies momma's. I am an American by choice, I am a son, I am a brother, I am a military service member, I am a man who has lost complete faith in the system, when the system betrayed, slandered, and libeled me. I lived a good life and though not a religious man I always stuck to my own personal code of ethics," he wrote. "I didn't need the US Navy to instill Honor, Courage, and Commitment in me but I thank them for re-enforcing it. It's in my DNA."
Dorner says he grew up in Norwalk, California, neighborhoods with small black populations and was "the only black kid" in his classes through seventh grade. He was disciplined for fighting as a youth, but only when classmates would call him racial epithets, he wrote.
He went to high school in the Los Angeles suburb of La Palma, where his mother still lives. Crystal Lancaster, who lives next door to the tan, stucco home, said it was "a big shock" to hear Dorner was the subject of a manhunt.
"We all couldn't believe it. We didn't know him that well, but he seemed like a really nice guy," she said.
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, the school's 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."
Usera, his Southern Utah classmate, also had many kind words for Dorner, who he said was "smart and insightful" and "a perfectly rational human being." But he also conceded his old pal could be recalcitrant.
"He was a person of conviction and when he made up his mind about something, right, wrong or otherwise, he made up his mind and you weren't going to convince him otherwise," Usera said.
Though Usera received an "out-of-the-blue" phone call from Dorner four years ago complaining about conditions at the LAPD, he sensed nothing that would have foretold the mayhem that has unfolded in the last 10 days.
"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.
But if everything police say about Dorner is true, Usera said he isn't necessarily surprised.
"I think (his stubbornness) may be one of the things that brought about his demise in this case. I don't think once he got going on this, frankly, this mission of vengeance that he was on, based on his personality type -- the way I knew him -- there was not going to be any good end to it," Usera said.
After college, Dorner joined the Navy, receiving a commission as an ensign in July 2002. He trained in river warfare units 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 also received several decorations, including the National Defense Medal, Iraq Campaign Medal, Global War on Terrorism Service Medal, Sea Service Deployment Medal and Navy Marine Corps Overseas Service Ribbon.
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 Dorner's manifesto, he flatly blamed the LAPD for costing him his naval and law enforcement careers, but again doesn't elaborate, and says he has tried everything possible to restore his good name.
"I lost my position as a Commanding Officer of a Naval Security Forces reserve unit at NAS Fallon because of the LAPD," he wrote. "I've lost a relationship with my mother and sister because of the LAPD. I've lost a relationship with close friends because of the LAPD. In essence, I've lost everything because the LAPD took my name and new (sic) I was INNOCENT!!!"
He calls his rampage "my last resort," according to the manifesto.
Dorner writes that he knows that people who have been acquainted with him will be surprised by "media reports that I am suspected of committing such horrendous murders and have taken drastic and shocking actions in the last couple of days."
He goes on to even predict the nice things that would be said about them and assure the purveyors of those comments that he had no other choice.
"You are saying to yourself that this is completely out of character of the man you knew who always wore a smile wherever he was seen. I know I will be villified (sic) by the LAPD and the media. Unfortunately, this is a necessary evil that I do not enjoy but must partake and complete for substantial change to occur within the LAPD and reclaim my name."
CNN's Eliott C. McLaughlin, Alan Duke, Mallory Simon, Matt Smith, Barbara Starr and Anderson Cooper contributed to this report.