Search for answers in psych scan

DAYS AFTER bullets rained down from a hotel in Las Vegas, little is known about the motives behind the deadliest mass shooting in modern U.S. history.

Investigators are hopeful that a “psychological autopsy” of shooter Stephen Paddock will help make sense of the madness.

FBI Deputy Director Andrew McCabe said Wednesday it is a “surprise” that agents have yet to uncover any clues as to what led Paddock to open fire on a crowd of concertgoers, killing at least 58 people.

“Those are the questions obviously that we are focused on right now,” McCabe said. “This individual … didn’t leave the sort of immediate thumbprints you find on these kinds of attacks.”

Investigators are busy reconstructing the 64-year-old’s life and behavior, and tracking down the people he encountered in the weeks leading up to the mayhem, McCabe said.

“We’ve got to look into his background,” said Gregory Vecchi, assistant professor of criminal justice with Missouri Western State University in St. Joseph, Mo. “Where are the problems? Look for the losses in his life.”

Paddock fatally shot himself in the head before cops broke into his 32nd-floor hotel room.

If his brain remained intact, an autopsy could find potential neurological issues that may partially explain what sparked the carnage, retired FBI profiler Jim Clemente told The Associated Press.

A “psychological autopsy” — looking at mental health history, substance problems, run-ins with the law enforcement — could also play a role in the investigation.

“Medical examiners rely on it when there are questions about the events which led up to the death,” Jim McCauley, associate director of the Riverside Trauma Center in Needham, Mass., told the Daily News. “There is an attempt to understand the state of mind of the deceased during the days and weeks leading up to the event.”

Paddock, a high-roller with an arsenal of high-powered weapons, left no manifesto or indication why he took aim at the crowd below his Mandalay Bay hotel room window on Sunday.

A source told ABC News that Paddock rapidly lost weight in recent weeks and became increasingly obsessed with his girlfriend’s exhusband, signs that he was “descending into madness.”