More than 10 months after the deadliest mass shooting in modern U.S. history, police say they are closing their investigation without answering the key question: What drove a gunman to unleash a hail of gunfire that killed 58 people and wounded hundreds more?

An Arizona man who sold ammunition to the gunman in the deadliest mass shooting in modern U.S. history was charged Friday with manufacturing armor-piercing bullets, according to court documents obtained by the Associated Press.

An Arizona man named in court documents as a “person of interest” during the investigation of the worst mass shooting in modern U.S. history said Tuesday he had met the shooter one time and sold ammunition to him.

The Las Vegas gunman meticulously planned the worst mass shooting in modern U.S. history, researching SWAT tactics, renting other hotel rooms overlooking outdoor concerts and investigating potential targets in at least four cities, authorities said Friday.

Legal action following the mass shooting at a Las Vegas concert is picking up with lawsuits filed Wednesday on behalf of 14 concertgoers, including some who were shot or injured trying to escape and one woman who is so traumatized that she has since mistaken the sound of rain for gunshots.

The costs of emergency police, fire and other services related to the Las Vegas shooting massacre were projected Wednesday at about $4 million and climbing.

The gunman who unleashed the deadliest mass shooting in modern U.S. history first wounded an unsuspecting hotel security guard in a hallway who promptly radioed for help, according to a TV interview broadcast Wednesday with the guard and a hotel building engineer whose life he is credited with saving.

The hotel security guard wounded by the Las Vegas shooter inside a hotel before the concert massacre canceled scheduled TV interviews last week because of a medical appointment, a missed appearance that raised questions about the whereabouts of a key witness to the deadliest shooting in modern U.S. history.