ISIS has claimed responsibility for the attack at an Afghan wedding hall in a Shi'ite neighborhood.
"A rational observer may have brushed off Trump’s tweets as hyperbole, but Mr. Sayoc took them to heart," his attorneys wrote.
“We can be glad that the farmer was not in the field,” a city spokesman said of the weekend blast.
Although Christians are currently a minority in Sri Lanka, Christianity has a long history in the island nation.
The nationwide social media blockage came after eight blasts swept through Sri Lankan churches and hotels on Easter Sunday, killing more than 200 people.
More than 500 people were also wounded in the attacks.
President's son cranks up insulting rhetoric after bombs were mailed to his father's opponents.
He "was attracted to Trump reaching out to these types of outsiders ... telling them that it’s okay to get angry," said Ron Lowy.
Fifteen people were taken to the hospital, three of them with critical injuries.
Ariana Grande, Prince William and victims' families remembered those lost their lives in last year's Manchester bombing.