The provided evidence includes web search results mentioning the claim, but these results are generic or unspecific ('Volunteer Community: Volunteer Community Loading Sorry to interrupt CSS Error Refresh'). No multiple independent news sources or authoritative references corroborate the specific details about assembling a weapon near the terrace-level entrance. The evidence is insufficient to corroborate the claim across multiple sources.

The claim is directly supported by one web search result mentioning Helen Mabus, a volunteer from Harrisburg, Pa., describing a 'makeshift room' near the entrance with bar carts and lack of security. No other independent sources corroborate this specific testimony.

The claim is supported by web search results referencing Helen Mabus stating the weapon was retrieved from a bag and was long and not like a typical gun. No other independent sources corroborate this specific testimony.

The claim is supported by web search results referencing Mabus stating the suspect was partially out of view of security while handling the weapon inside the room before moving toward the main event space. No other independent sources corroborate this specific testimony.

The claim is supported by web search results referencing Mabus stating the gunman assembled the weapon and ran toward the stairs leading to the ballroom. No other independent sources corroborate this specific testimony.

The claim is supported by web search results mentioning the gunman firing in multiple directions as guests and staff attempted to escape. No other independent sources corroborate this specific testimony.