A Secret Service internal review of the failures that led to the attempted assassination of former President Donald J. Trump at a July 13 rally in Butler, Pa., found that agents did not have the necessary discussions about how a complex of warehouses surrounding the site should be protected.

The most glaring of the agency’s security lapses on that day centers on how an armed 20-year-old was able to climb onto a roof of one of the warehouses, giving him a clear line of sight to Mr. Trump. Other failures noted in the agency’s summary include the inability of the Secret Service to talk with its local partners over radios and technical challenges that prevented agents from launching drone detection on the day of the rally.

The Secret Service’s findings were released in a brief summary of its monthslong inquiry on Friday. The complete report is not yet finished.

The abbreviated findings left some major questions unanswered, including: Who in the Secret Service was responsible for ensuring that the warehouses were properly protected on the day of the event? And why didn’t any agents in the agency’s communications hub realize that they were not hearing from local police radios in the hours they were there before Mr. Trump took the podium?

“It’s important that we hold ourselves to account for the failures of July 13 and that we use the lessons learned to make sure that we do not have another mission failure like this again,” the agency’s acting director, Ronald L. Rowe Jr., said in a statement before a news conference on Friday afternoon.

The attempted assassination of Mr. Trump in July — made by a man named Thomas Crooks who fired off eight rounds — was the first instance of a current or former president being shot since 1981. Mr. Crooks was able to graze Mr. Trump’s ear before being killed by a Secret Service countersniper’s bullet. Three rally attendees were also shot, one fatally.

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