A third suspect arrested in connection with an alleged plot to derail a passenger train travelling between Toronto and New York discussed contaminating the air or water with bacteria in an effort to kill up to 100,000 people, documents show.

According to a U.S. Department of Justice document, Ahmed Abassi, who was arrested on April 22, suggested using the bacterial agent in his discussions with another terror suspect and an undercover FBI agent.

Abassi, a Tunisian citizen who has lived in Canada, was charged with fraudulently applying for a work visa in order to remain in the United States to facilitate an act of international terrorism.

U.S. authorities unsealed the charges against Abassi on Thursday.

“As alleged, Ahmed Abassi had an evil purpose for seeking to remain in the United States – to commit acts of terror and develop a network of terrorists here, and to use this country as a base to support the efforts of terrorists internationally,” U.S. attorney Preet Bharara said in a statement from the U.S. Department of Justice.

Late last month, RCMP had arrested two men -- Chiheb Esseghaier and Raed Jaser -- on several terror-related charges in connection with the alleged plot. Both men are currently in custody until their next court appearance, scheduled for May 23.

The FBI alleges that Abassi “radicalized” Esseghaier and that the two men met in New York City at one point.

But Abassi didn’t know that one of his associates, with whom he shared his alleged terror plot, was an undercover FBI agent.

Authorities said Abassi was under surveillance “at all times” since his mid-March arrival in the U.S.

Abassi kept in regular contact with the undercover FBI agent, referred to as “UC,” authorities said.

“During Abassi’s discussions with Esseghaier and with the UC, which were recorded by the UC, Abassi discussed his desire to engage in terrorist acts against targets in the United States and other countries, and his intention to provide support and funding to organizations engaged in terrorist activity – including the al Nusrah Front, which is recognized by the U.S. Department of State as an alias for al Qaeda in Iraq – and to recruit other individuals for terrorist plots,” the FBI said in a statement.

According to the Department of Justice’s letter to a U.S. district judge, Abassi told the undercover agent that Esseghaier’s proposed terror plots were “good,” but “the time was not right.”

Abassi said he suggested contaminating the air or water with bacteria in order to kill up to 100,000 people, but “Esseghaier was dismissive of that plan,” according to the document.

The FBI alleges that, on April 12, Abassi told the undercover agents about his efforts to recruit other terrorists. He also said that he might be able to get documents to remain in the U.S. under the pretense of working for the undercover officer’s company.

Abassi is charged with two counts of knowingly making false statements in an application to the immigration authorities for a green card and work visa, in order to facilitate an act of international terrorism.

Each count carries a maximum prison sentence of 25 years.

In a statement, the RCMP said it worked “very closely” with the FBI on the parallel investigations in Canada and the U.S.

“Through our efforts, we assured that at no time did this individual pose an imminent threat to public safety in Canada,” Sgt. Greg Cox said.

Cox said the Mounties won’t be providing any further information about their investigation because the case is now before the courts.

Esseghaier, 30, and Jaser, 35, are charged with conspiracy to commit murder, participating in a terrorist organization and conspiracy to interfere with transportation facilities.

In addition, Esseghaier is charged with one count of having directed a person to carry out a terrorist activity.

CTV News has reported that Esseghaier, a Tunisian-born PhD student in Montreal, had travelled to Iran within the past two years.

Jaser, a Toronto-area resident, was almost deported from Canada in 2004 because of fraud convictions. But because he was listed as a stateless Palestinian, Canadian authorities had nowhere to send him.

Jaser’s family came to Canada in 1993 with fake French passports. The family claimed they faced persecution in Germany, but their request for asylum in Canada was denied.

Although most of Jaser’s family members ended up obtaining Canadian citizenships, Jaser could not follow suit because of his criminal record.

In addition to fraud convictions, Jaser was convicted of uttering threats. He received a federal pardon in 2009, CTV News has reported.

The RCMP has alleged that Esseghaier and Jaser received "guidance" from al Qaeda in Iran, but said the plot was not state-sponsored.

The accused’s lawyers and family members have said that the men are innocent.