Investigators trying figure out why Stephen Paddock gunned down 59 people from his high-rise hotel suite are analyzing his computer and cellphone, looking at casino surveillance footage and seeking to interview his longtime girlfriend.

Nearly two days after the deadliest mass shooting in modern U.S. history, what set off the 64-year-old high-rolling gambler and retired accountant remained a big question mark Tuesday.

While the probe into his background included searches of two houses he owned in Nevada, some investigators turned their focus from the shooter’s perch to the killing grounds outside the Mandalay Bay hotel casino where his victims fell.

A dozen investigators, most in FBI jackets and all wearing blue booties to avoid contaminating evidence, entered the festival site where gunfire erupted Sunday night and country music gave way to screams of pain and terror.

“Shoes, baby strollers, chairs, sunglasses, purses. The whole field was just littered with things,” said Nevada Attorney General Adam Laxalt, who told The Associated Press it was like a “war zone.” ”There were bloodstains everywhere.”

Paddock killed himself before a SWAT team blew off the door of his room on the 32nd floor. He had 23 guns with him at the hotel — along with devices that can enable a rifle to fire continuously, like an automatic — and 19 more guns at one of his homes, authorities said.

More than 500 people were injured in the rampage, some by gunfire, some during the chaotic escape. At least 45 patients at two hospitals remained in critical condition.

Retired FBI profiler Jim Clemente speculated that there was “some sort of major trigger in his life — a great loss, a breakup, or maybe he just found out he has a terminal disease.”

Clemente said a “psychological autopsy” may be necessary to try to establish the motive for the attack. If the suicide didn’t destroy Paddock’s brain, experts may even find a neurological disorder or malformation, he said.

He said there could even be a genetic component to the slaughter: Paddock’s father was a bank robber who was on the FBI’s most-wanted list in the 1960s and was diagnosed a psychopath.

“The genetics load the gun, personality and psychology aim it, and experiences pull the trigger, typically,” Clemente said.

Paddock had no known criminal record, and public records showed no signs of financial troubles, though he was said to be a big gambler.

“No affiliation, no religion, no politics. He never cared about any of that stuff,” his brother, Eric Paddock, said outside his Florida home. He said he was at a loss to explain the massacre.

Nevada’s Gaming Control Board said it pass along records compiled on Paddock and girlfriend Marilou Danley to investigators. Danley is expected to speak with detectives when she returns to the U.S. from out of the country.

The FBI discounted the possibility of international terrorism early on, even after the Islamic State claimed responsibility for the attack.

The Las Vegas gunman who killed nearly 60 people at a country music festival worked as a letter carrier for the U.S. Postal Service, an IRS agent and in an auditing department over a 10-year period.

A spokeswoman for the Office of Personnel Management told The Associated Press on Tuesday that Stephen Paddock’s employment included about two years as a mail carrier from 1976 to 1978.

After that, he worked as an agent for the Internal Revenue Service for six years until 1984. And then he worked a defense auditing job for about 18 months.

The information helped complete the timeline surrounding the 64-year-old Paddock’s life. He graduated from college in 1977 from Cal State Northridge and also worked for a defense contractor in the late 1980s.

On the surface, Paddock didn’t seem like a typical mass murderer, said Clint Van Zandt, a former FBI hostage negotiator and supervisor in the bureau’s behavioral science unit. Paddock is much older than the typical shooter and was not known to be suffering from mental illness.

“My challenge is, I don’t see any of the classic indicators, so far, that would suggest, ‘OK, he’s on the road either to suicide or homicide or both,” Van Zandt said.

Nevertheless, his actions suggest that he had planned the attacks for at least a period of days.

Some of the rifles had scopes, the sheriff said. And authorities found two gun stocks that could have let him modify weapons to make them fully automatic, according to two U.S. officials briefed by law enforcement who spoke on condition of anonymity because the investigation is still unfolding.

“He knew what he wanted to do. He knew how he was going to do it, and it doesn’t seem like he had any kind of escape plan at all,” Van Zandt said.

Asked about a potential motive, Sheriff Joseph Lombardo said he could not “get into the mind of a psychopath at this point.”

“I can’t even make something up,” his bewildered brother, Eric Paddock, told reporters Monday. “There’s just nothing.”

Public records offered no hint of financial distress or criminal history, though multiple people who knew him said he was a big gambler.

“No affiliation, no religion, no politics. He never cared about any of that stuff,” Eric Paddock said as he alternately wept and shouted. “He was a guy who had money. He went on cruises and gambled.”

Eric Paddock also told The Associated Press that he had not talked to his brother in six months and last heard from him when Stephen checked in briefly by text message after Hurricane Irma. Their mother spoke with him about two weeks ago, and when he found out recently that she needed a walker, he sent her one, Eric Paddock said.

Eric Paddock recalled receiving a recent text from his brother showing “a picture that he won $40,000 on a slot machine. But that’s the way he played.”

He described his brother as a multimillionaire and said they had business dealings and owned property together. He said he was not aware that his brother had gambling debts.

“He had substantial wealth. He’d tell me when he’d win. He’d grouse when he’d lost. He never said he’d lost $4 million or something. I think he would have told me.”

Heavily armed police searched Paddock’s home Monday in Mesquite, about 80 miles northeast of Las Vegas near the Arizona border, looking for clues. Paddock lived there with his 62-year-old girlfriend, who authorities said was out of the country when the shooting happened. Eric Paddock described her as kindly and said she sometimes sent cookies to his mother.

Police also searched a two-bedroom home Paddock owned in a retirement community in Reno, 500 miles from Mesquite.

(AP)