State Attorney General Alfredo Castillo said that the group’s involvement was identified from a partially destroyed note found at the scene.

Castillo said the group opposes experiments with nanotechnology and has staged attacks on academics before.

A manifesto signed by the group and posted on a radical website said: “We have no remorse, our aim was precisely for the guards to deliver the package to the intended professor,’’ whom it identified as Oscar Camacho.

A Web page operated by Mexico’s National Polytechnical Institute listed Camacho’s research as including “micro-electro-mechanical systems.’’

The group’s statement said Camacho’s inspecting the package triggered the detonator.

The statement said nanotechnology damages nature and native species and contributes to natural disasters.

The group said it had struck before, claiming it left another bomb at another university, and suggested the bombing would not be the last.