But he was devastated on returning from the Philippines to find that the bag, which was unmarked, had been thrown out with the rubbish in a clear-out of his laboratory.
"To some people it might have been just a bag of lizard shit," he told Times Higher Education.
"But to me it represented seven years of painstaking work searching the rainforest with a team of reformed poachers to find the faeces of one of the world's largest, rarest and most mysterious lizards.
"Its loss left me reeling and altered the course of my life forever."
The butaan is closely related to the komodo dragon, although it is extremely reclusive, so methods usually used to study the komodo are not suitable for the butaan.
The University has offered him 500 pounds (730 dollars, 570 euros) in compensation and an apology, after the student lodged an official complaint about the loss.
But Bennett says this is not enough, and has vowed to "see them in court".
"Whether it was the largest collection of lizard shit in the world is uncertain," he said.
"But it certainly contained the only dietary sample from that little-known species Varanus olivaceus, and probably the most complete dietary record of any single population of animals in South East Asia."
In a statement the university said: "The loss of these samples was an unfortunate mistake. They were thrown away in error because they were in an unmarked bag.
"Lessons have been learned and protocols improved to ensure this cannot happen again. Mr. Bennett is due to graduate with his PhD this year, subject to minor corrections to his thesis unrelated to the loss of the materials."
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Image of Komodo dragon, by Andrew Yates.
"To some people it might have been just a bag of lizard shit," he told Times Higher Education.
"But to me it represented seven years of painstaking work searching the rainforest with a team of reformed poachers to find the faeces of one of the world's largest, rarest and most mysterious lizards.
"Its loss left me reeling and altered the course of my life forever."
The butaan is closely related to the komodo dragon, although it is extremely reclusive, so methods usually used to study the komodo are not suitable for the butaan.
The University has offered him 500 pounds (730 dollars, 570 euros) in compensation and an apology, after the student lodged an official complaint about the loss.
But Bennett says this is not enough, and has vowed to "see them in court".
"Whether it was the largest collection of lizard shit in the world is uncertain," he said.
"But it certainly contained the only dietary sample from that little-known species Varanus olivaceus, and probably the most complete dietary record of any single population of animals in South East Asia."
In a statement the university said: "The loss of these samples was an unfortunate mistake. They were thrown away in error because they were in an unmarked bag.
"Lessons have been learned and protocols improved to ensure this cannot happen again. Mr. Bennett is due to graduate with his PhD this year, subject to minor corrections to his thesis unrelated to the loss of the materials."
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Image of Komodo dragon, by Andrew Yates.