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The gunman who terrorized a quiet Houston neighborhood Sunday before a SWAT officer shot him dead was an Army veteran who served in Afghanistan and was suffering from depression, officials and family said Tuesday.

Dionisio Garza III, 25, had left San Bernardino County, California, for Texas last week to see friends in the area, Houston police said. But the trip turned into a shooting rampage in which Garza fired off 212 rounds and left another person dead and six others wounded, including two officers.

Garza "suffered from some depression," authorities told reporters. "His family indicated he wasn’t feeling right and came here to hang out with his friend."

Dionisio Garza III via Facebook

"It appears to be someone who was in a mental health crisis," officials added.

As investigators work to determine a motive for the attack, police laid out how the random scenario unfolded.

Garza purposefully "went off the radar" from his family and friends Saturday afternoon after arriving in Texas, and had broken into a tire shop, police said. On Sunday morning, he confronted a customer identified as 56-year-old Eugene Linsomb.

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Related: Investigators Search for Motive Behind Houston Shooting Rampage

Garza ended up fatally shooting Linsomb. He then grabbed his AR-15 and began spraying bullets at cars driving by as well as police officers who arrived at the scene amid reports of an active shooter at 10:15 a.m., police said.

Garza also struck a line at a nearby gas station, causing a fire.

A SWAT team member eventually ended the chaos when he struck the gunman from over 100 yards away.

Another armed man identified as John Wilson was initially thought to be a possible second suspect, but police said Tuesday that he was a Good Samaritan trying to stop the shooter. Wilson was shot in the leg but survived.

"What he did was very brave, but officers are trained in these active shooter situations (but) he was outgunned, out-maneuvered," said acting Houston Police Chief Martha Montalvo.

She advised the public instead to "call the police and let us do what we have to do."

Police said Garza had left "random writings" on the wall of the tire shop, but declined to divulge the messages. They also wouldn't comment on reports that he made disparaging remarks against homosexuals and Jews amid his rampage, and was confident there was "no hate crime" involved.

Garza's family in California told NBC affiliate KPRC that he was different following his two tours in Afghanistan.

He first went there from 2009 to 2010, and then again from 2012 to 2013, reaching the rank of sergeant in December 2011, records show. He was discharged in 2014.

Family members said he appeared to be suffering from post-traumatic stress disorder.

"Something snapped. It wasn't him anymore," Garza's father, also named Dionisio Garza, told KPRC. "I'm not making excuses. No excuses. I know he did this, but it wasn't him anymore. My son was broken."

Garza's mother said the family was extremely tight and he was very "loving," but his attitude toward life took a turn in the past couple of weeks as he became convinced that the world was ending.

She was still searching for answers for the bloodshed being blamed on her son — what she doesn't know, she said, is "why."

"I'm sorry for what happened. I'm sorry to the families," Michelle Garza said. "Words are just words. I wish there was more that we could do."