Raymond Boodarian — the man accused of committing the grisly double homicide of “American Idol” music supervisor Robin Kaye and her husband Thomas Deluca in a botched burglary — had long alarmed his neighbors with alleged bizarre and erratic behavior … TMZ has learned.

We spoke with multiple neighbors who live in the same Los Angeles apartment complex where Boodarian resided with his mother, stepfather, and teenage sister — and where he was taken into custody on Tuesday. All described disturbing encounters with the 22-year-old, and they claim he regularly walked around the complex in a trance-like state.

The neighbors tell TMZ he would wander the property for hours, sometimes barefoot, just staring at the ground. The neighbors said he never seemed present, and recalled him always being “out of it.”

Neighbors say he’d often knock on random doors in the complex, asking for people who didn’t even live in the unit, lie in the grass seemingly zoned out, and would frequently argue loudly with his family inside their unit. “There was always yelling coming from their apartment — mostly him screaming at his parents,” one said. The neighbors described the rest of his family as always polite and kind.

After Boodarian’s arrest, his mother and sister left the complex. His stepdad — who works in construction, according to neighbors — has been seen around since. It’s understood among neighbors that Boodarian didn’t have a job … he was described as not a normal-acting person who always seemed like he might be on substances.

Despite the unsettling behavior, some residents were blindsided to learn he’s now suspected in the gruesome double murder. “He was definitely strange, but I never imagined this,” said one neighbor.