The US Department of Agriculture (USDA) inspector general is investigating Neuralink for possible animal abuse violations related to research testing. As reported by Reuters, internal documents show that employees have expressed concern that the company rushed into animal testing, causing them to suffer and die.

Since 2018, the company has reportedly killed 1,500 animals, including more than 280 sheep, pigs and monkeys. These numbers do not automatically mean that Neuralink is breaking the law, and the company has passed all inspections of its facilities by the USDA. However, former and current employees told Reuters that pressure from Neuralink founder Elon Musk to speed up development led to failed experiments and thus a higher-than-necessary death rate.

Musk is also reported to have asked employees since the company’s founding in 2016 to imagine they had a bomb strapped to their head in an attempt to get them to move faster. He also told employees he would trigger a “market crash” if they didn’t make progress, which some employees interpreted as a warning that he would shut down the company. Earlier this year, Musk also sent an email to employees with an article about Swiss researchers who created an implant that helped a paralyzed man walk again, Reuters reported.

“Generally, we’re just not moving fast enough. It’s driving me crazy!” he wrote in the following e-mail.

After reviewing internal testing documents, Reuters reported that it found four experiments involving 86 pigs and two monkeys with results that were called into question due to human error. Neuralink had to repeat these experiments, which resulted in even more deaths. A message written by an angry employee talked about how rushed animal surgeries had led to under-prepared and overstressed employees who ended up making mistakes.

Several examples seen in the documents by Reuters detail how Neuralink employees implanted a brain-machine interface device into the wrong vertebra of two different pigs — something that could have been easily prevented by counting the animals’ vertebrae — and had the team kill them to end their suffering.

Earlier this year, the animal rights group Physicians Committee for Responsible Medicine accused Neuralink of botched surgeries that killed monkeys. The company admitted it killed six monkeys in its joint study with UC Davis because of problems caused by their experiments. However, they defended their research and stated that it did not break any laws.

Neuralink recently held an event where it announced it could begin human trials within the next six months. During the program, founder Elon Musk directly responded to the accusations of the Committee of Physicians:

“Before we would even think of putting a device in an animal, we do everything possible we with rigorous benchtop testing, We’re not cavalier about putting these devices into animals. We’re extremely careful and we always want the device, whenever we do the implant — whether into a sheep, pig or monkey — to be confirmatory, not exploratory,” he said.

Reuters, however, said it found Neuralink records with numerous references to “exploratory surgeries.” Autumn Sorrells, Neuralink’s Animal Care Program Director, also reportedly ordered employees in October to remove “exploration” from their study titles and to stop using the term going forward.