[Robe]

From: About.com Guide:
The prisoner is strapped to a chair inside a sealed gas chamber. The executioner (standing outside of the chamber) pulls a lever dropping potassium cyanide pellets into a vat of sulfuric acid, flooding the chamber with lethal hydrogen cyanide gas.

If this guy put the water in the paint can and then heated it .. would that produce a lethal gas??

[a fool in paradise]

If this guy put the water in the paint can and then heated it .. would that produce a lethal gas??

I don't know the particulars of cyanide gas.

The terrorists in the 1993 WTC bombing used it. Except the exploding van incinerated the gas that was supposed to fumigate the stairwells.

[sig226]

No. The reaction used to release the cyanide in a gas chamber is a classic reduction-oxidation reaction. Sodium cyanide plus sulfuric acid produces hydrogen cyanide and sodium sulfate.
Na(CN) + H₂(SO₄)=2H(CN)+Na₂(SO₄)
You need the highly reactive hydrogen ions in the acid to get the lethal gas. If he ate the sodium cyanide pellets, they would have killed him, but the stuff he had would not cause a lethal gas attack. This may mean he really was suicidal, or that he was poorly informed like the idiot with the Times Square bomb.