Story highlights Witness heard jumper say 'All right, let's do this' before running toward fence

Secret Service says suspect scaled fence as first family celebrated Thanksgiving inside

Witnesses say the man was draped in an American flag and was carrying an envelope

(CNN) A man is in custody after jumping over a White House fence while the first family was inside celebrating Thanksgiving, officials said.

Joseph Caputo scaled a fence on the North Lawn at 2:45 p.m., according to Secret Service spokesperson Robert Hoback. The jumper was immediately apprehended and taken into custody.

According to two CNN photojournalists who witnessed the incident, the men was carrying an envelope, had on a blue shirt and white pants and was cloaked in an American flag. They said the officers who detained him had their guns drawn and were accompanied by K-9 units.

Vanessa Pena, an intern on Capitol Hill, was playing tourist with her twin sister who was in town for Thanksgiving. "We were just standing there and the man came up behind us," she told CNN. "I heard him take a deep breath and say, 'All right, let's do this.'"

Pena said the man "ran through" she and her sister before he jumped over a barricade, and then the fence.