THE mother of a student found dead in a field with a date-rape drug in his system is considering hiring her own detective.

Donna O'Halloran, 41, said she was disgusted to learn police had concluded their inquiry into the death of her son, David.

The 18-year-old, a first-year student at Stirling University, was found dead in April, three months after having vanished following a night out with friends.

Toxicology tests in ­Glasgow last week concluded he had high levels of GHB in his blood, urine and hair.

Ms O'Halloran, from Kilmaurs, Ayrshire, said yesterday: "Someone did this to him, and in my eyes that makes this manslaughter. And, rest assured, somehow I will find out. A private detective is one way."

Police Scotland said their inquiries into the David's death "have now concluded".

A spokeswoman added: "We are aware of the suggestion David's drink may have been spiked, but our investigations have shown there is no evidence to prove this."