Las Vegas gunman Stephen Paddock, who killed 58 people in the deadliest mass shooting in modern U.S. history, lost hundreds of thousands of dollars gambling and spent $95,000 on firearms purchases in the year before last year’s Oct. 1 attack, according to the final report on the massacre by Las Vegas police.

The report, released Friday, gives the most detailed look at Paddock’s finances to date, and offers new information about his declining health and lack of intimacy with his girlfriend—but makes no conclusion about what...