Experts say they are baffled by the discovery of mustard gas in Roughton Moor Woods near Woodhall Spa.
A police cordon still remains in place around the woods more than a week after the canisters were discovered on Sunday October 1, apparently by two history enthusiasts.
In a swiftly moving saga, two people were taken to hospital and released after treatment for minor burns and respiratory problems.
Within hours, police had arrested two people from the Lincoln area where they also searched a property.
A third person - a man from the Woodhall Spa area - was also arrested. A property in Woodhall Spa was searched on the same day.
All three were detained on suspicion of possessing a noxious substance but were released on police bail.
Attention then switched to a search of a private lake at Stixwould near Woodhall Spa.
Before the News went to press yesterday lunchtime, emergency services were still based at the lake and the woods.
Police said contaminated items were being taken away for examination.
Police stress there is no danger to the public and that their work is designed to make the areas safe.
Sources suggest officers have yet to discover why the gas canisters were found in the area.
Graham Keegan, a renowned local historian, expressed his surprise.
Mr Keegan explained mustard gas was used during the First Word War, killing and injuring thousands of soldiers.
According to Mr Keegan, there were no troops stationed in the Woodhall Spa area in WW1.
Thousands of troops were billeted in the woods in World War Two but by then, mustard gas had been outlawed by the Geneva Convention.
There was an RAF base located near the woods in WW2 but again, there is nothing to suggest any chemical weapons were housed there.
Mr Keegan told the News: “I would be quite staggered if there was any mustard gas in the Woodhall Spa area during WW2.
“That’s not to say it wasn’t stored somewhere because it is something the military might not hold their hands to.
“People are quite rightly asking whether there is an isolated find or whether it’s a chemical weapons dump.
“What has happened raises more questions than answers.”
Several residents contacted the News to say they regularly walked their dogs in Roughton Woods but had never seen any suspicious objects.
People living near the site complained a couple of months ago that a WW2 bomb had been detonated without notice.
Meanwhile, police are warning the public to stay clear of the woods.
Chief Inspector Dan Whyment said: “We appreciate this is a frustrating time for people who want to enjoy the woods but we ask you to just bear with us for a little while longer.
“Work is likely to continue into next week and possibly beyond. We’re very much aware that people want to see the woodland reopened and we’re doing our best to make sure that this happens as soon as possible.”