Federal officials, including the FBI, questioned a Texas man on Thursday night in connection with what are believed to be three ricin-laced letters sent to President Barack Obama, New York City Mayor Michael Bloomberg, and his gun control group Mayors Against Illegal Guns.
The letters to Bloomberg tested positive for ricin, while the letter to Obama is still being tested, but thought to contain the deadly poison.
Authorities also went to the man's New Boston, Texas home where they removed computer equipment and other items, according to KSLA-TV in Shreveport, La.
The man, who has not been identified, is a person of interest but has not yet been arrested.
Ricin is a poison that is extremely deadly, and even the amount contained in a pinhead, about 500 micrograms, can be enough to kill a person according to OSHA.gov.
A source told ABC News that the man's wife "called authorities after she noticed strange material in her refrigerator, and noticed computer searches for ricin."
More from GlobalPost: New ricin letter sent to Obama: Secret Service
The threatening letters to the President and Bloomberg's gun-control group in Washington had identical text that read:
"You will have to kill me and my family before you get my guns... Anyone wants to come to my house will be shot in the face. The right to bear arms is my constitutional God-given right and I will exercise that right 'til the day I die. What's in this letter is nothing compared to what I've got planned for you."
Both letters were postmarked May 20 from Shreveport, La.