Boston, Apr 25 (IANS): Vice President Joe Biden has described the two Boston Marathon bombers as "twisted, perverted, cowardly knock-off jihadis" who failed to instill fear in the American people.

"It infuriates them that we refuse to bend, refuse to change, refuse to yield to fear," Biden said at a memorial service in Cambridge, Massachusetts, Wednesday honouring slain Massachusetts Institute of Technology police officer Sean Collier.

"The doctrine of hate and oppression, they've found out cannot compete with the values of openness and inclusiveness. And that's why they're losing around the world."

Collier was allegedly shot in the head execution-style by the two suspected bomber brothers. Tamerlan and Dzhokhar Tsarnaev, while sitting in his patrol car on April 18, three days after the Boston Marathon bombings that killed three people and wounded hundreds.

The vice president also offered counsel to the larger campus community, still reeling from the blasts, shooting, and manhunt that swept their neighbourhood last week.

"Just look around this field at the student body here," Biden said. "Just listen to the accents of the president and vice president. This is a diverse campus. Probably the greatest technological university in the world. It's black, it's white, it's Muslim, it's Christian, it's Jewish, it's Hindu."

"You make no distinction between the competence of male and female. You are their worst nightmare. All the things these perverted jihadis, self-made or organized, all the things they fear," he continued.

Later in the day, Biden's wife Jill, dressed in black, visited a memorial site on Boylston Street, near the blast site in Boston.

She hung a pair of black running shoes, signed "Boston Strong. Love, Jill Biden," on a police fence covered with other running shoes, flowers and big posters memorialising the victims of last Monday's attack.