Mr Le Guillou died on 10 August last year, three days before his 55th birthday.
His brother-in-law – who did not wish to give his own name – said: “The police gave very good support, but mental health nothing.
“I think its back-up support was atrocious.”
Responding to his brother-in-law’s comments, Mr Weir said mental health staff normally did provide support to families after a patient’s death and pledged: “I will go away and find out what happened and why it happened.”
Pictured: “I will go away and find out what happened and why it happened,” said Andy Weir.
The inquest heard that Mr Le Guillou, who was divorced and lived alone, was highly intelligent and had been very good with working with his hands, but had suffered mental health problems for many years.
Medical and support staff were aware that he had previously expressed suicidal thoughts and feelings.
Mr Le Guillou’s brother told the inquest that he had spoken to him by phone the day before he died but he had seemed perfectly normal.
A post-mortem showed there were no drugs or alcohol in Mr Le Guillou’s system.
Relief Coroner Sarah Whitby said there was no evidence of “obvious gross failure” in Mr Le Guillou’s death, and returned a verdict of suicide.