from what i have gathered, this is part of a research programme held in collaboration with the national institute of education (nie). when the reptile was captured, they would first syringe some blood from it. the lizard would be put to sleep with a lethal injection. in the laboratory, they would dissect the big lizard to study the content in its gut.
on the topic of catching monitor lizards, my friend nah once told me that the foreign workers, especially the thais, used a simple loop to trap the monitor lizards that lived on the banks of the kallang river. they would set up the trap overnight and collect their booty the next morning. the thai workers did not catch the monitor lizards to keep as pets. i have been told that the meat of the lizard tastes better than chicken's meat.
another friend of mine, who served as a camp instructor on pulau tekong some 30 years ago, claimed that the taste was akin to that of chicken meat. one of the islanders would trap the lizard and cook it himself. he added some herbs were used to get rid of the fishy taste.