Arriving in Alaska from Puerto Rico in the midst of her divorce proceedings, Santiago began living with her in an apartment along Mockingbird Drive by early 2015, according to court documents.
Bill Peterson said that he "didn't want to let my kids around" Santiago, but he never learned much about the young man's relationship with his ex-wife.
"I stay out of her private life. That's hers," he said.
FBI agents have told the gaggle of national journalists circling her Medfra Street home to forgo knocking on the door. The cameramen catch sporadic sightings of her, in between visits from federal agents.
Her 18-year-old daughter, Robyn Peterson, read a brief statement on her behalf and those of other relatives to the scrum of reporters gathered at the home on Monday evening.
"My deepest condolences to the innocent people who lost their lives and/or were injured," she read, adding that the family "all hope that the victims see justice."
She then asked for privacy while the entire family mourned.
In November, Santiago brought their newborn baby with him to the Federal Bureau of Investigation field office in Anchorage. He told authorities that the government was trying to control his mind and forced him to watch Islamic State terrorist videos — an interview that triggered a call to the Anchorage Police Department, the confiscation of his 9mm semiautomatic handgun and the return of the baby boy to Peterson.
He told law enforcement interrogators in Florida that doctors told him during an involuntary but brief November stay in an Anchorage mental health facility that he may have schizophrenia, sources told the Sun Sentinel.
On Feb. 23, 2015, Gina Peterson and Santiago were evicted from the Mockingbird Drive apartment and ordered to pay $929 in back rent, court documents state.
Ticketed for a broken taillight and driving without insurance, he also had been fined $1,060 but struggled to repay the bill. In mid-2015, it was sent to collections.
According to his brother Bryan, Santiago was working at an Anchorage McDonald's and supplemented his wages one weekend per month drilling with the Alaska Army National Guard.
He had enlisted in August of 2014 and was assigned to the Guard's 1st Squadron of the 297th Cavalry Regiment, according to Guard spokeswoman Lt. Col. Candis Olmstead.
Santiago was not a cavalry scout by training. He joined the Puerto Rico Army National Guard in late 2007 and became a combat engineer. He deployed to Iraq for a 10-month tour that straddled 2010 and 2011.
Although the Alaska reconnaissance squadron was headquartered in Fairbanks, it maintained a company of soldiers at the sprawling Joint Base Elmendorf-Richardson in Anchorage.
Guard officials refused on Monday to say whether Santiago was supposed to attend drill weekends in Anchorage or travel as far as 250 miles north to Fairbanks.
In October, the cavalry squadron was converted into an infantry battalion and placed under the command of a brigade in Hawaii.
After their 2015 eviction, Santiago and Peterson settled into the squat Medfra Street home in the Fairview section of Anchorage.
On Jan. 10, 2016, Santiago began yelling at her when she was on the toilet. Breaking through the door and smashing the frame, he ordered her to get out "while strangling her and smacking her in the side of the head," according to the criminal complaint filed in the wake of the assault.
The officer saw "no physical injuries" on Peterson.
Arrest logs showed that he stood 5 feet 8 inches tall and weighed 140 pounds. Peterson was eight inches shorter and 20 pounds heavier, according to her previous Domestic Violence Court documents.
Arraigned before a magistrate two days later, Santiago was barred from having any contact with Peterson. The arraignment judge specifically allowed Santiago to possess weapons.
Free on a $1,000 unsecured bond, Santiago took up temporary residence at a trailer park along Dimond Boulevard in Anchorage.
On March 24, 2016, Santiago pleaded to both assault and criminal mischief charges as part of a deferred sentencing agreement.
Although ordered to complete a 12-week anger management program, there is no indication in the court documents that he finished the course.
He was granted unlimited contact with Peterson if she allowed it. She apparently did, according to neighbors, but the couple kept to themselves and Santiago seemed distant but polite. He spent much of his time working on his car. On New Year's Eve, the couple threw a party.
"He wouldn't look me in the eyes usually," said Perette Carter. "He'd usually say, 'How you doing, ma'am,' and then just, like, look away."
Carter and other Fairview neighbors said that he never mentioned Florida.
"That's the puzzle. Why Florida? He was just here on New Year's Eve, talking."
It's unclear when Santiago left their Medfra Street home, but he was living in a discount motel in an Anchorage neighborhood known for drug trafficking, prostitution and panhandling shortly before he bought the airline tickets that would take him to Florida.
In August, shortly before his son was born, Santiago was involuntarily separated from the Guard under a "general" discharge for "unsatisfactory performance," according to military spokeswoman Olmstead.
He was transferred to the Inactive Reserve as a private first class. That's one or two ranks below where he should have been after nearly a decade in the Guard, but both Olmstead and Pentagon officials have declined to comment on Santiago's final months in the Alaska squadron.
His military awards included the combat action badge, Army commendation medal and the good conduct medal, suggesting eight years of unblemished service before he joined the Alaska Guard.
When asked if he had frequently been absent without leave on drill dates or committed any other infraction that would terminate his military contract, Guard officials referred all questions to the Pentagon.
Officials there said that they needed to research the issues and have yet to respond to questions.
Sun Sentinel staff writers Paula McMahon, Sally Kestin and Megan O'Matz contributed to this report.
Carl Prine, a reporter for the San Diego Union Tribune, is on assignment for the Sun Sentinel.
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