MILFORD, Pa. — An antigovernment survivalist charged with ambushing two troopers at a State Police barracks did research on how to avoid searchers more than a year before the deadly attack, according to evidence presented Monday at his murder trial.

Eric Frein’s laptop was used to search online for ‘‘how to escape a manhunt’’ and ‘‘how are manhunts conducted’’ in May 2013.

Frein avoided capture for 48 days before US marshals caught him at an abandoned airplane hangar more than 20 miles from the Blooming Grove barracks in northeastern Pennsylvania, where, authorities say, he killed Corporal Bryon Dickson II and critically wounded Trooper Alex Douglass on Sept. 12, 2014.

The survivalist claimed to police on the night of his arrest that he had planned the sniper attack only a few days earlier, but his Internet search history suggests he had been mulling it over for a lot longer.

Other searches from May 2013 included ‘‘bug out cache’’ and ‘‘tips on placing caches,’’ presumably of food and other supplies.

Frein used the Internet while he was on the run, too, performing dozens of searches of his own name, alone and in conjunction with words like gun, evidence, and manhunt. He sought out his wanted poster and did research on Dickson, according to the testimony.

And, prosecutors say, he wrote to his parents. The letter, read to jurors Monday, spoke of revolution and said, ‘‘The time seems right for a spark to ignite a fire in the hearts of men.’’ Frein, 33, pleaded not guilty.

Associated Press