The site of the explosion at Derrinallum.

The site of the explosion at Derrinallum. Photo: Victoria Police

Bomber Glenn Sanders visited a Ballarat hospital wearing a vest believed to be filled with explosives on several occasions before he blew himself up at his Derrinallum farm – and police were warned about it.

Mr Sanders visited his sick mother at St John of God hospital with the vest strapped to his chest every day for at least four weeks before he triggered the April 12 explosion that killed him and injured two policemen.

A lifelong friend, Derrinallum plumber Gary Poole, said he told police Mr Sanders was wearing a device that potentially contained explosives into the hospital, but they took no apparent action.

Glenn Sanders.

Glenn Sanders. Photo: Allan Warren

"It wasn't just a one-off time that he wore the vest to hospital. He did it all the time," said Mr Poole.

"I can't believe I was contacted by Ballarat police several weeks before the incident with Glenn but nothing was done.

"They raised questions with me about a vest he was wearing. I confirmed that he had a vest and I believed it contained explosives.

"I told them I couldn't guarantee whether they were real or fake but I have seen enough explosives and detonators in my time to believe they were real.

"I warned them that I didn't want to read in the newspaper about an explosion going off in the hospital."

Acting Superintendent Paul Ross said police had received reports of incidents involving Mr Sanders since the middle of last year and action was taken then.

A police spokeswoman said investigations were continuing.