The packages arrived in everyday manila envelopes affixed with lots of stamps, some bearing the American flag. But what was inside was alarming: crude pipe bombs wrapped in black tape, with wires sprouting from each end.
None of the explosives detonated, and no one was hurt, but authorities quickly launched a wide-ranging investigation into the devices that targeted multiple Democrats - including two former presidents - and foes of President Donald Trump's administration ahead of the 6 November midterm elections.
Here is what we know so far:
- Hillary Clinton and two former presidents
All the confirmed bombs appeared to come from the same person or persons, said John Miller, New York Police Department's head of intelligence and counter-terrorism, who briefed reporters in the city.
The Secret Service intercepted a bomb addressed to Ms Clinton at the home she shares with former president Bill Clinton in Chappaqua, New York, and another that was sent to former president Barack Obama at his family home in Washington.
Neither the Clintons nor the Obamas received the packages, and none had been at risk of receiving them because of screening procedures, the Secret Service said.
Overhead TV shots showed that device, which law enforcement officials said was linked to the other explosives, being driven away. The package contained a live explosive and an envelope with white powder, and the substance was being tested to see if it was dangerous, authorities said.
Two law enforcement sources said the device was crude but operational. It was addressed to former CIA director John Brennan, who regularly appears as a television contributor and who has publicly clashed with Mr Trump.
The president and his aides routinely criticise CNN over its coverage, and he calls the network an example of fake news.
- George Soros
A suspicious device was found on Monday at the New York compound of the billionaire who is a major contributor to Democratic causes.
An official said investigators believe the explosive discovered near the Clintons' home was linked to the one at the compound.
- Debbie Wasserman Schultz
All the envelopes listed representative Ms Schultz as the return address. The FBI also said it was responding to a report of a suspicious package at one of Ms Schultz's offices in Florida.
She is the former chairwoman of the Democratic National Committee who was accused by Clinton rivals of secretly boosting the former secretary of state to the party's 2016 presidential nomination.
The envelopes, only a few inches long, had typed letters and six stamps that bore no cancellation mark.
- Eric Holder
The FBI says Mr Holder, the country's chief law enforcement officer for most of the Obama administration, was the intended target of a device that was similar to the others but was sent to the wrong address.
- Maxine Waters
The FBI said two additional packages addressed to Ms Waters had been intercepted that were similar in appearance to five others.
The outspoken Democrat representative is frequently criticised by Mr Trump. He has called her "an extremely low-IQ person" and has pegged her level of intellect as "somewhere in the mid-60s", which is considered the range for a mental disability.
She has called him "the poster boy for what a mob protester looks like".
- What we do not know
How dangerous the devices were.
The pipe bombs were packed with powder and shards of glass. The devices, each with a small battery, were made from PVC pipe about 6in long and covered with black tape, said a law enforcement source who viewed X-ray images.
Officials do not know if there are other devices out there, undelivered.
- "Mob" politics
The discovery of the devices comes at a tense time, with Republicans and Democrats casting each other as a "mob" that would do anything to win or keep control of Congress in two weeks.
Mr Trump has a history of advising supporters to "knock the hell out of" protesters and saying he would like to see opponents carried out "on a stretcher". Last weekend, he said at a rally in Montana that a congressman who body-slammed a Guardian reporter was "my kind of guy".
As the scope and targets of the device deliveries became clear, Mr Trump called them "despicable acts".
"Acts or threats of political violence of any kind have no place in the United States of America," he said during an event at the White House.
"This egregious conduct is abhorrent to everything we hold dear and sacred as Americans," he added. "We're extremely angry and upset and unhappy about what we witnessed this morning, and we will get to the bottom of it."
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