Last May, congressional staffers started with a very simple question: Exactly how easy is it for the average person to order some of the deadliest drugs on the planet over the internet and have them delivered to their home from the other side of the globe?

The answer, they revealed this week, is: shockingly easy.

At a briefing on Wednesday several Senate investigators working for Sens. Rob Portman (R-OH) and Tom Carper (D-DE) detailed to reporters exactly how simple it is to order fentanyl, a synthetic opioid that has overtaken heroin and prescription painkillers to become the biggest killer of Americans, online.

The staff started, quite literally, by Googling “fentanyl for sale,” they said. They found pages and pages of advertisements. Posing as first-time buyers, they made contact with six responsive sellers. These sounded like sophisticated operations, offering discounts on bulk purchases and even trying to upsell the investigators to carfentanil, an even more powerful opioid.

The sellers preferred Bitcoin, the investigators said, but they also accepted Western Union transfers, PayPal, and prepaid credit cards. They wanted to ship the packages through the international arm of the US Postal Service, rather than a private carrier like FedEx or UPS. They told the investigators that there was less of a chance the package would end up detained.

At one point, when China cracked down on a specific strand of fentanyl, the sellers advertised “a hot sale” on the top of the email, which the staff included in their report, literally said: “JUNE SPECIAL OFFER” – to try to empty their reserves before the ban went into effect.

Using payment and shipment information that the sellers themselves provided, the Senate investigators identified 500 transactions in 43 states adding up to $766 million worth of fentanyl, going by its street value, just from these six sellers. They found people who were purchasing for personal use – including seven who overdosed and died – as well as the people buying to set up their own distribution network in America.

It became clear how adaptable the fentanyl sellers were. Now that shipments from China have come under suspicion, the sellers told the investigators that they preferred to ship through Europe. Even as the US worked with China to crack down on one fentanyl compound, the sellers simply tweaked their formula and offered to sell a new version in another email included in the report.

The underlying message of the report was that the US Postal Service should do more to crack down on these illicit shipments. Right now, private carriers are required to collect advanced electronic data, a bar code with information about the sender, the recipient, and what is in the package. But the Postal Service and its foreign counterparts do not. That’s precisely why sellers prefer the US Postal Service over FedEx or UPS.