New York Mayor Michael Bloomberg not intimidated by ricin-laced letters

(CBS News) Federal investigators are trying to figure out who sent two threatening letters laced with the deadly poison ricin to New York City Mayor Michael Bloomberg and his gun-control group in Washington.

CBS News correspondent Elaine Quijano reports that authorities say responding officers who came into contact with the letter in New York suffered some minor symptoms. No one was seriously hurt, but now a joint terrorism task force, including the FBI and the NYPD, is investigating.

Bloomberg spoke with reporters shortly after the threats against him became public Wednesday evening.

"No, I'm not angry," said Bloomberg. "There are people who, I would argue, do things that may be irrational, do things that are wrong, but it's a very complex world out there, and we just have to deal with that."

On Friday, a worker at a mail facility in lower Manhattan intercepted a letter addressed to Bloomberg that was laced with ricin - a highly toxic poison.

Another tainted letter was discovered two days later in Washington at a building that houses Mayors Against Illegal Guns - a non-profit group Bloomberg helped start. That envelope was addressed to the group's director, Mark Glaze.

Both mailings were postmarked May 20 from Shreveport, La., with no return address.

They contained a pink-orange, oily substance, and each letter threatened bodily harm against the mayor and made references to his stance on gun control.

A law enforcement official told CBS News the letter addressed to Bloomberg said something along the lines of "this is a taste of what's to come if you come to take my gun."

The mayor has emerged as one of the country's leading gun-control advocates and just this year helped pay for TV ads urging Congress to approve background checks.

CBS News senior correspondent John Miller reports from a conference of police chiefs in Dallas that the ricin investigation isn't the only threat worrying New York Police Commissioner Raymond Kelly. Instead, Kelly fears terrorists are gaining momentum.

(Watch Miller's report at left)

Bloomberg said this latest threat won't intimidate him.

"There's 12,000 people that are gonna get killed this year with guns and 19,000 that are going to commit suicide with guns, and we're not going to walk away from those efforts," Bloomberg said.

Investigators are conducting more tests to confirm the presence of ricin.

This is just the latest in a string of similar incidents. Last month, a Mississippi man was arrested for trying to send ricin-laced letters to President Obama, a U.S. senator and a judge.

Watch Elaine Quijano's full report in the player above