The New York Police Department and officials from the city departments of Health and Environmental Protection responded to the scene, along with the Office of Emergency Management.
Donald Jr.'s wife, Vanessa, opened the envelope and discovered the powdery substance and note, sources said.
She then dialed 911, saying she was coughing and feeling nauseous.
Honour Colten Boushie by fixing broken justice system
Cries and rants of "MURDERER!" flooded social media, as did shouts of "RACIST!" towards those who agreed with the jury's verdict. They allege the officers were callous in how they informed the family of Boushie's death and then immediately searched the home.
The US Secret Service, which is charged with protecting members of the president's family, has joined the investigation, said spokesman Jeffrey Adams. Out of caution, officials say investigators will conduct a thorough probe of the event. The apartment may be the home of Vanessa Trump's mother, local news outlets reported.
(Photo by Win McNamee/Getty Images) Donald Trump Jr, his wife, Vanessa, and children depart St. John's Church in Washington, DC, after a service for U.S. President-elect Trump on January 20, 2017. This is the reason why people hate you.
The New York Daily News reported slightly different wording: "You're an terrible person and now you get what you deserve".
Judge Dismisses 'Player Hater' Copyright Suit Against Taylor Swift
The plaintiffs' song includes the following line in the chorus: " Playas, they gonna play, and haters, they gonna hate ". Responding to the allegations previously, a spokesperson for Swift had said that it was a "money grab".
NYPD later determined that the white powder was harmless. The New York Post reported that the material was cornstarch. The couple has five children; none of the kids were home at the time of the incident. Nonetheless, the letter itself was threatening.
Investigators confirmed that the mysterious white substance inside the envelope was corn starch.
UK police investigating unspecified incident in parliament
An unnamed police officer in Speaker's Court in Parliament said a suspicious package has been found. Most MPs are not in Westminster this week as Parliament is in recess for school half-term.
Donald Trump Jr. praised first-responders and investigators yesterday thanking them via Twitter "for their decisive action and incredible words of support to my wife and family". "Truly disgusting that certain individuals choose to express their opposing views with such disturbing behaviour".