Aircraft manufacturer Boeing and the American aviation authority FAA get it in a report by the transport committee of the House of Representatives on the Boeing 737 MAX.
Two aircraft of that type crashed shortly after each other.
The committee researched the development of the aircraft for a year and a half.
"Boeing failed to design and develop the MAX and the FAA failed to oversee Boeing and certify the aircraft," the 250-page report released Wednesday.
The investigation report lists numerous shortcomings on the part of both parties.
The Boeing 737 MAX aircraft have been grounded worldwide since the last crash in March last year.
According to the new report, the crash of the two planes - the first crashing in October 2018 - was not the result of a single shortcoming or technical error, but a "poorly managed event".
"There was a horrific accumulation of incorrect technical assumptions by Boeing engineers, a lack of transparency on the part of Boeing's management and gross shortcomings in the FAA's oversight," the report said.