Officials on Sunday confirmed the identity of the UN worker.
"He was identified this morning and his family has been informed," UN spokeswoman Ariane Quentier said.
One of the three victims appeared to be the bomber, because of severe body mutilation, police said.
The third fatality and five people wounded were Afghan customers.
"We suspect it was an attack on an Internet cafe, where foreigners go to check their mail," an Interior Ministry spokesman said. "It might be a terrorist attack, but it's still too early to say."
Police have detained five people including the owner of the cafe for questioning, he added.
The attack was the first to kill a UN official in the capital since the fall of the Taliban in 2001, and added to tension already high in Kabul because of concern that criminal groups might try to kidnap foreigners.