WASHINGTON (Reuters) - Investigators believe that the design and instructions for building the bombs sent to several critics of U.S. President Donald Trump this week were taken from the internet, a federal law enforcement official told Reuters on Thursday.

The instructions for such devices are widely available on websites and in propaganda distributed by Islamic militant groups including Al Qaeda and ISIS, said the official and a former federal government bomb expert.

The federal official also said the designs could have been lifted from “The Anarchist Cookbook,” a notorious bomb and hacker manual dating to the early 1970s.

There was no claim of responsibility for the spate bombs, none of which exploded.