Harvard Medical School released a statement this afternoon, saying the endangered monkeys it shipped in a van to the Oregon Zoo "arrived safely and in good condition."

Six of the nine cotton-top tamarins died in the zoo's quarantine on May 24. Documents first reported today by WW show the monkeys died after traveling more than 50 hours in a van, and spent their final days in plastic picnic coolers zoo officials gave them as nests.

Gina Vild, chief communications officer for Harvard Medical School, sent a statement to WW defending the shipment of monkeys by van, along with records showing the monkeys were in good condition throughout the trip.

"The standard and safest method of transporting nonhuman primates in North America is through experienced ground carriers," the statement says.

Harvard Medical School also gave WW a letter sent to its officials by the Oregon Zoo's head primate keeper Jennifer Davis, speculating that the plastic coolers might have killed the monkeys with "some sort of off-gassing like effect."

Harvard's copy of Davis' May 28 letter redacts her name but identifies her by her title, "curator of primates and Africa." She suggests that the monkeys that died had spent more time in the coolers than the ones that lived.

"They had been fully cleaned and disinfected and dried," Davis writes of the coolers. "Perhaps there was some sort of off-gassing like effect? Coolers certainly smell weird all on their own. It's just all speculation and questions at this point."

Harvard University had been widely reported as the donor of the monkeys to the Oregon Zoo, but the school and the zoo had refused until now to confirm where the monkeys came from.

Here is the full statement from Harvard Medical School:

We were deeply saddened to learn about the unfortunate event at the Oregon Zoo related to the cotton top tamarins. While we typically do not comment on transports, we feel it is important to share these documents that show the animals arrived at the Oregon Zoo safely and in good condition on Thursday morning, May 22. These documents include the animal health observation log, the USDA 7020 form that acknowledges receipt of animals, and two email exchanges.  The standard and safest method of transporting nonhuman primates in North America is through experienced ground carriers. The carrier is registered with the USDA, and it provided environmentally controlled, door-to-door transportation that met all USDA guidelines.  In accordance with the Animal Welfare Act, the animals were observed every four hours during transit, and were provided fresh produce, water and food at intervals that met USDA regulations.