Investigators have still not discovered what motivated Stephen Paddock to embark on the worst mass shooting in modern U.S. history but determined that he researched SWAT tactics ahead of the massacre and investigated other possible targets, including the famed California beach in Santa Monica, officials said Friday.

Story continues below

They also determined that Paddock acted alone when he opened fire from his high-rise hotel suite, killing 58 people and injuring hundreds, Clark County Sheriff Joe Lombardo told reporters.

READ MORE: California couple who survived Las Vegas shooting die in vehicle crash

Lombardo made public a preliminary report into the shooting and said he does not expect charges to be filed against Paddock’s girlfriend, Marilou Danley, who had been previously called a person of interest in the case. Investigators also found that Paddock had possessed child pornography, Lombardo said.

READ MORE: Brother of Las Vegas shooter, Bruce Paddock, detained in child porn investigation

Paddock’s online searches before the shooting included research into SWAT tactics and for other potential public venue targets — and he took photographs of some potential sites, the sheriff said. The searches also included the number of attendees at other concerts in Las Vegas and how many people go to Santa Monica’s beach.

The sheriff and the FBI have said they found no link to international terrorism. They said they believe Paddock meticulously prepared and concealed his plan to fire assault-style weapons from the 32nd floor of the Mandalay Bay hotel into a crowd of 22,000 people attending the Route 91 Harvest Festival music below.

Paddock fired more than 1,100 bullets, mostly from two windows in the high-rise hotel, Lombardo has said. That includes about 200 shots fired through Paddock’s hotel room door into a hallway where an unarmed hotel security guard was wounded in the leg and a maintenance engineer took cover to avoid being hit.

Several bullets hit aviation fuel storage tanks at nearby McCarran International Airport that did not explode. Authorities reported finding about 4,000 unused bullets in Paddock’s two-room suite, including incendiary rounds that Lombardo said were not used.

Investigators found 23 guns in the rooms, including 12 rifles that a federal Bureau of Alcohol, Tobacco and Firearms official said were fitted with “bump stock” devices that allowed rapid-fire shooting similar to fully automatic operation.

READ MORE: Las Vegas gunman Stephen Paddock was emailing about bump stocks for months: documents

Paddock killed himself with a gunshot to the mouth before police reached him. The 64-year-old retired accountant and multimillionaire real estate investor had earned hotel upgrades as a high-stakes video poker gambler at several Las Vegas casino resorts.

Danley was in the Philippines at the time of the shooting.

Lombardo and Aaron Rouse, FBI agent in charge in Las Vegas, had described Danley as a person of interest in the investigation but not a suspect. She was questioned by the FBI when she arrived in Los Angeles from overseas, and was described as cooperating with investigators.

WATCH: Newly-released audio sheds light on timeline of Las Vegas shooting

However, a document filed Oct. 6 and unsealed last Friday by a federal judge in Las Vegas said the FBI considered Danley “the most likely person who aided or abetted Stephen Paddock.”

Questions have been raised about Danley’s receipt in the Philippines of a $10,000 wire transfer from Paddock just days before the shooting.

FBI warrant documents also showed that Danley told investigators that they would find her fingerprints on bullets used during the attack because she would sometimes help Paddock load high-volume ammunition magazines, and that Danley deleted her Facebook account in the hours immediately following the shooting.

The Clark County coroner ruled that all 58 people killed in the attack died of gunshot wounds. Paddock’s death was ruled a suicide. Media organizations including The Associated Press are seeking autopsy records that have not been made public.

Read the full report here: 

___

Balsamo contributed from Los Angeles.