The man arrested in Florida last week in connection with the rash of crude pipe bombs sent to outspoken critics of President Trump had been planning his campaign for at least three months, and his laptop and cellphone are now providing investigators with a trove of fresh evidence, new court papers say.

Calling the bomb spree “a domestic terrorist attack,” prosecutors gave a glimpse into its origins, describing in the court papers how the laptop of the suspect, Cesar A. Sayoc Jr., had been used, as early as July, to draft a list of targets and scour the internet for information on them.

The new court papers were addressed to a judge in Miami where Mr. Sayoc, 56, is set to appear this week at a bail hearing. Prosecutors in Manhattan are expected to ask a judge to detain him pending trial, and, in the filing, asked that Mr. Sayoc be sent to New York City for prosecution and denied bail on the grounds that he posed a “substantial danger to the community and a significant risk of flight.”

After an intense, nationwide manhunt, Mr. Sayoc, an ardent fan of Mr. Trump, was taken into custody on Friday in a parking lot in Plantation, Fla., near a white van in which he had apparently been living.